Personally, I think you'd have to be utterly crazy and suicidal to buy bootlegged aircraft plans on ebay or elsewhere. Can the seller guarantee that all the safety critical amendments and mandatory mods have been embodied? Can they f--k! Most likely they don't even know or care of such things, their significance and their consequences. I read on another forum recently, someone asking whether it was a good idea to buy laser eye surgery via ebay. FFS - some people!
On the other hand, I have been able to get a complete pdf workshop manual for my classic car from one such seller. It did bother me because it is abuse of copyright, but this manual is no longer available by any legitimate means. It is extremely handy to be able to print of the relevant page and take it down to the garage when doing a bit of maintenance. Fortunately it is not quite the same as building an autogyro from plans bought from a stranger and bootlegger who know nothing about aero engineering or regulation.