One good thing is, a lot more people have a decent camera these days, so just take a big close-up shot in good light, and paste it up on here, and let the real pros deliberate
I handled most weapons as a kid, and still have about 75% of those, but finding out recently about all the sculpt variations was pretty enlightening, that's for sure. Take the Endor Commando rifle for example. I had only ever known, for 27 years, the very detailed, very fragile version, but buying a few of these guys recently, I have seen the much thicker, slightly less detailed one in browner plastic.
A site like TIG is very good, but there's still gaps that need filling, especially the cape section. The ERG staff info on there mentions the fake one not matching up on both sides, but I have been stung with one that did, but was perfectly straight, and had a slightly different marking at the top. That's a £5 weapon loose, so you can see the reasons why these horrible bootleggers create hard to spot fakes, and flood the market. The older, painted brittle plastic stuff is much easier to detect as long as you have handled a few legit Kenner accessories. I don't know of any fake blasters yet that are translucent when held up to the light, like the original plastic is on many of them.
What is worrying, is that some of the eBay sellers peddling this stuff, have 100% feedback, with many vintage SW related transactions. Who the hell is buying it all, and not complaining? Same deal with guys on there vastly exaggerating the condition of their loose figures, with C-9 items arriving with loose limbs, dirt on them, pen marks or paint rubs. If people don't learn and object to these practices, then it will just continue. Ideally, eBay would have a real Kenner collecting expert patrolling the vintage section... but don't hold your breath for that!