I would always recommend caution and research when purchasing through such places that may not offer any provenance behind the desired piece. That being said, it is good to know some of the common traits within bootleg figures. Historically bootlegs tend to have a far less quality difference when compared to their licensed counterparts. Packaged bootlegs often lack manufacturing company (i.e. Hasbro, Kenner) as seen in below:
To the untrained eye, these figures may appear to look like Engineering Pilots. However, they are poor quality knock-off figures in which also lack Kenner logos.
Today, there are higher quality bootlegs like this Russian Bossk figure. To the untrained eye, it may look like a first shot prototype. However, it is currently around a $20 find and are very plentiful. Prices can also be a red flag.
So, research is key! I think joining Star Wars bootleg Facebook groups is a good way to understand what is out there in terms of bootlegs. You are certainly welcome to post any questionable pieces in this forum. There are many seasoned prototype collectors on here that can help you identify the legitimacy of an item.