It's a game. We play it to have fun.
Ask the players why they are doing these work-a-day jobs. If it's because they enjoy it, then by all means keep on enjoying oil changes. If it's because they're not having fun due to a dearth of funds, you need to make the game fun. Make 'em earn it, of course, but you can earn good pay with any character - it's the GMs job to make sure of this (i.e. tailor the game to your players, challenge them, make it interesting, but let them play - not work), this premise of the "level of the job" is an entirely subjective premise and is not a part of any metric other than the one you make up at your table (which should be made up to fit your players). You can do million dollar jobs out of the gate if you want to (i.e. if that's the M.O. of the table), the only reason you should ever have your PCs doing oil changes is if they find it fun.
After 1 run (you did say you've only done 1 run, right?), they may just not have an idea of what's coming (and hopefully better things are coming) and are just feeling insecure for the moment (which is fine, for now), but if they persist in trying to earn money doing mundane jobs, I'm sorry - if there's 1 thing I hate, it's people telling people how to play the game - but chances are they aren't doing it for fun, or character development, and if they're not having fun why are you playing?
(I can't believe A4BG and I agree on something...)