Something that is sleazy is low and nasty. It’s a perfect word to describe characters like the sleazy door-to-door con men who cheat old ladies into selling them their jewelry at a deep discount.
Sleazy originally meant flimsy, but nowadays it’s only used to describe morally degraded people or places. Usually it refers to sexual behavior, but it is often associated with people trying to swindle others as well. It’s not as bad as perverse or criminal, which suggest that a line has been crossed. But sleazy people make you feel uncomfortable, for sure.