I've only been scammed one time and that was atleast 2 years ago, i was trying to buy a rune scimmy and i derped into the bait and switch with a mith scimmy. Back then that was a tone of money for me =( Now its like i wipe my ass with it ;)
Personally id make my own Prayer potions, just because the market seems to flux in that area a lot, and if you dont drink them in the time that they rise up, sell it for a better profit then you would if you sold asap. If their is one thing i learned from this game, dont sell right away, wait for the market to upturn, and sell 2 days after it rises.