buying from whole seller pros and cons

Hi Bp...was thinking recently to buy a property from a whole seller...not sure if anything I need to avoid or be cautious about before getting myself into contract...I noticed most of the whole sellers not all of them...they way under estimate the rehab and pick the highest comps or some times they base their ARV on the for sale properties available on the market not the sold comps !!! I'm trying to understand the whole thing since its gana be my first time using this method.

Any insight would be appreciated.