You forget just how good the Sith are at mind control such things. There are Sith in EU that can pretty much possess and make mind slaves of underlings and other such pepole.
When a Jedi uses a Mind Trick, it is usually more of a 'Oh feck, need to get out of this situation...' type of thing. Obi-Wan for example, in ANH; he doesn't want to get caught by stormies, he doesn't want Luke arrested, he doesn't want the droids captured.
Qui-Gon's instances; he needs to get off of Tatooine, and fast, or he needs to get to the Queen fast. The Mind Tricks just help the situation along. With Watto, he didn't have the local currency, but he WAS going to pay with credits; it's just that credits didn't matter to Watto. With Nass, Nass wasn't going to help him and Qui-Gon was pretty much just going to be arrested or something. Instead, Nass gives him a submarine.
Palpatine pulls a Mind Trick on Grievous in LoE...now THAT was Mind Control...
Still, it's not like the Jedi will say 'You WILL give me your wallet...' or 'You WILL have sex with me...' and other such dire things.