Do what I've been doing to see if certain skills raise. First, look at the progress bar for Speech and take note of how filled in it is. Then take your 20 pelts or whatever and sell 10 of them one at a time. Exit the barter screen and convo, and then go back to check on your Speech bar. Make note of how much it's filled now. Then go back and sell 10 more, bu this time all at once. Check your progress bar again and compare it to how much it changed the first time.That should answer your question. If you are close to gaining a level in Speech, then you might want to try this with 4-5 items each time.
Yep - had 20 wolf pelts. Saved before selling. Sold all 20 - speech bar moved a tiny bit.
Loaded save. Sold all 20, one at a time - gained a level and almost filled the bar again.
So tedious, but I guess it will be worth it in the end.
(and yes, I loaded it a second time, and converted the wolf pelts (3g) to leather (4g), and sold it for more)
Thanks for the idea.