The subject of recast models can be a fairly dodgy subject to discuss as there's no concrete way of proving a figure is a recast or not apart from complicated metal composition testing I would imagine but that's beyond me and most others I think and it'd probably involve the dissection of the fig anyway.
There are certain tell-tale signs though which lead to models being suspicious and there's always EBay history too which may help as you can see if someone has sold 20 of the same Unreleased models in the last year or 2.
Before we get onto the tell-tale signs it'd probably be best to start with a bit about where the recasts are mainly coming from. I say mainly as I know from dealing with people on forums that there are recasters everywhere in the world and the majority are just making their own moulds to cast their own figs for personal use. Its inevitable that some of these will end up getting sold on EBay etc at some point as collectors\gamers die and houses get burgled etc. So don't think that because you are just doing it for personal use its not causing a problem, unless you destroy those figures at some point you will probably be adding to the problem. Obviously casting resin copies of metal figs or making plaster versions for scenery etc isn't a part of the problem as anyone can tell its not the real thing and there's no conning going on. It may be against copyright laws but no real damage is being done in my opinion but that is just my opinion of course.
So although recasting goes on everywhere there are 2 main places in the world where the majority of the recasts for sale are coming from and they are Russia and China. I know China has no Intellectual Property laws so anything can be copied and sold and I assume Russia is the same or doesn't enforce the copyright laws at least. Countries surrounding Russia like Ukraine are also known for recasts coming from them and I assume many Eastern European countries will be the same so I'm not saying don't buy from these places, just be very wary when dealing with companies or people from there. Just because they are a web-based shop doesn't mean they aren't selling recasts, you can easily buy recasts and the unofficial Legandarion sculpts from their website and E-Minis has even been suspected of selling recasts and they're based in Spain.
Considering China has no IP laws its a wonder that companies like GW\Forgeworld want to base their production there but they do and they are only driven by profit these days so cheap production is paramount and ethics no longer matter to them. Its hard to feel sorry for a company that only cares about profits or anyone who thinks business doesn't have responsibilities for that matter. Fake GW figures coming out of China may well be produced on the same production line as the real ones though so does that make them really fake? Its a conundrum.....Legacy Miniatures may well be based in China too and they did the castings of the CMON Confrontation range so its possibly not isolated to GW unfortunately. I cannot find out where Legacy are\were based so do not take this as fact.
Japan, although very near to the counterfeit capital of the world is generally regarded to be a fairly safe place to buy figures from. Honour is a very big part of the Japanese culture so maybe this plays a part.
Now onto the suspicious signs of a recast fig. I have experience of buying recast Games Workshop Dwarfs from a couple of EBay sellers and I also have the real figs so I have been able to do some comparisons with them. Recasts seem to be slightly smaller, if the real one is 28mm scale then the copy will be 26mm roughly. Not easy to spot if you just have one but quite obvious in a side-by-side comparison. I think this is to do with mould shrinkage but I'm not a caster so I'm just guessing. Another thing seems to be the tabs on the figs, probably where the shrinkage occurs the tabs seem to be noticeably thinner too but again easier to spot next to real thing. I'm sure its possible to make a mould and have no shrinkage or minimal at least so just because figure is the same size doesn't mean its real, I'm just saying that if its noticeably smaller then its probably a fake. Another thing I have noticed is a lack of detail in crevices and corners of the recast figs. Ok there's not much detail in most corners and crevices but on certain models, mainly ornate hero type ones, then you can notice it.
The colour of the metal cant always be relied upon as lots of things can change the colour of the metal since it was bought, paints, paint removers, salty sea air. However, having an old pre-slotta fig cast in white metal would probably raise a few eyebrows. The newer the fig the harder it is to judge by the metal I'd say and don't forget GW and other companies re-issued old 80's figs in newer metal and also sold moulds off to other companies for their use so you have to consider lots of things.
Miscasts are also not reliably recasts either, I remember people ordering Mid-Nor Dwarfs direct from Rackham and having figs turn up with split shields and all sorts of terrible miscast problems not to mention in wrongly labelled blisters too. They were always quick to send out replacements though I think but some people got replacements with the same miscasts which I found quite crazy.
If you think you have recast figures but want other opinions you can ask on many forums and the Yahoo CCM group is a good place to get expert feedback. Its not a good idea to go screaming "Re-caster" though, just give your suspicions and some photos to show what you mean and see what people say. Say who you are buying them from as the person may be well known as a collector or a re-caster but don't accuse them of anything as they could have been duped as well and they're just reselling whilst unaware of the problem.
I do not have any fake Rackham figs but I have never bought from Russia and I refuse to buy anything Chinese as I have imposed my own trade sanctions on them due to all the atrocities that are caused by and go on in that country. 99% of my collection is sealed in box\blister too so if anyone can add information on Rackham fakes I would be happy to post it here.
Legendarion may be considered a bit of a separate issue as although they are guilty of recasting, they have also sculpted their own figures albeit not under any licence. I personally don't have any problem with them doing this but I'm completely against them selling the recasts of figures they didn't sculpt. As Rackham are kaput and there's no support for the game I consider it acceptable but the figures they have done are based on artwork that someone did and I'm not sure how it sits with them. Konstantin from Legendarion contacted me to ask about this text and I am awaiting a reply from him where I will update this part as necessary, until he replies please be aware that for a long time they were offering recast GW figures along with recast Rackham figures and although they seem to have cleaned up their act people should still be aware they are recasting figures they do not own the rights to and therefore I think its considered illegal.
With 3d printing becoming more accessible, things are set for a big change as manufacturing figures in your home becomes a reality. Soon everyone will be able to print their own figures so its anyone's guess how this will affect our hobby. This will affect the whole world in a possibly bigger revolution than even the Internet has though so I think our hobby is the least of our worries.
These are just my opinions.