The lesson I have learned is to never buy MRR/RR/PLR if they don't spell out the rights you are buying prior to making a purchase. This is more of a problem more so with non-WF sources, as if someone here doesn't indicate the rights offered, generally another Warrior is quick to ask the question.
Some of these sellers will promise full MRR/RR and/or PLR rights, but then when you make the purchase and read the actual license agreement (if they even include one) you'll sometimes find that their definition of "full" and your definition are quite different.
And some degree of explicitness would be appreciated as well. For example, a product that cannot be given away free but can be given as a bonus. Okay, what if I offer a free bonus to someone signing up for my mailing list? Where does that fit in? Much simpler to have the YES/NO checkboxes that many WSOs have.
True, I can contact the seller, but, you know what? I really don't want to have to be contacting them all the time, after I have made a purchase, to find out what I can and cannot do with the product(s) I purchased. I want to know before I buy, or I'm not going to buy (anymore).
I think I will also avoid the products that say something like "This is valuable information and cannot be given away" because, maybe 9 times out of 10, the ones saying that are garbage that might be difficult to even give away for free and would likely have too high a return rate if you did offer it for sale. And, for the record, the ones I've come across like that were from non-WF sources.