"для" means intention. We do something for (для) achieving something else. Or we buy, keep, save something for (для) someone.
Whereas "за" usually means consequence. We thank people for (за) something, or kids are punished for (за) having done something wrong.
there are some exeptions though. For instance when we go to an election we vote for (за) someone. Also "за" can be used as "instead of".

btw, maybe you know, whether "body job" can ever mean "manual labour" or else what can it mean besides petting?

Thanks for clarifying that for me. I only know 'body job' to mean 'work done on a car', like 'nice body job on your truck.' I haven't heard it in a sexual connotation (only 'hand job').

or blow-job *in sexual connotation *

Oh yeah, that too. But body job is not a sexual term (in America to my knowledge). Just for cars, like many car repair shops are called "auto body shops."

> ...like many car repair shops are called "auto body shops."

Кто бы мог подумать, а!..