You don't. The only way to know you have an authentic Disney pin it so buy it yourself from an authorized
Disney store. The only pins Disney has made any noise about are not scrappers (over runs or copies of Disney pins), but rather out right counterfeits. Some CMs who collect pins themselves may recognize some of the most common counterfeits, although even then most of them will take the trade and then just set the pins aside instead of trading them back out.
If you're buying pins from anyone but Disney, or if you trade pins, you're at risk for getting a scrapper. But if the scrappers are of good quality, the same quality that Disney sells, and if Disney is not announcing which pins have been scrapped and asking people to watch for them, then it is not your job to watch for scrappers. Of course you don't want to pass on poorly made or defective pins, but you can buy one of those jewel gowned princess pins direct from Disney and end up with a pin that's missing some of the jewels -- the fact that it's an authentic pin doesn't mean you should trade with it.
Disney wants you to have fun trading pins and to be fair to others by not trading a pin you know is damaged. Disney is not asking you to be the scrapper police; if they wanted you to worry about scrappers, they'd be telling you what to look for, and what pins to avoid. Trading pins is supposed to be fun, not a source of worry. You're free to examine the pin yourself and make sure it's physically okay before trading, but there is no way for you, or usually for anyone, to be sure an authentic Disney design pin was originally sold by Disney or not when you trade for it.
If the fact that you got 2 "hidden mickey 6 of 6" pins from two different sellers is your only evidence that they're scrappers, then that is not sufficient evidence. I bought a bunch of pins that said the exact same thing last year from the outlet stores for less than a dollar apiece. Hidden Mickeys are not limited edition pins, and they're not hard to get, either by trading with cast members or by buying one of the mystery bags.