I feel like there has to be a take advantage of advanced scouting. Almost no one in my world pays for it. The issue is, I have no idea what prospects other franchises that don't pay for scouting are high or low on. Any tips for how to sell high and buy low on prospects?

you don't need to pay for advanced scouting, once you see the rate at which a prospect progresses each cycle that ratings update, you have a decent idea where he will end up.

most teams aren't trading their really good prospects anyhow. if you want to buy low or sell high, the trick is to value players who will get underrated at their peak and ship out the players who are going to be overvalued.