Do ou think sales jobs ruin people ?

Only if you were fake and manipulative going in.
If you are representing a crap product or service, then get out.
If you are representing a good product or service, sales can be very rewarding.

I stopped selling cars because i got tired of screwing people for a commission..
I'd sell a car at MSRP then sell a duplicate to someone else who had the sense to do some research for 3 or 4 thousand dollars less...

It got depressing after a while.

MLM jobs in particular.