He's definitely done some shady **** during his career. Marc Silvestri separated himself and Top Cow from Image because Liefeld was using company money to pay off personal debt. Then, when Liefeld had his Maximum Comics company outside of Image, he used Image artists for Maximum Comics promo work, tried to steal the artists away from Image, and didn't have a great record for paying artists for their work. He's also started **** with other comic book artists like Alan Moore and Rags Morales about the quality of their work. The Image founders didn't vote him out of Image for nothing.
All that being said, my personal interaction with him was this: I go to his booth to get a Deadpool print signed by him--which he was only at for a couple hours each day. He's reading something on his phone and doesn't acknowledge me even though no one else was there. After about 20 seconds I say "Hi" and he still doesn't look up for a few seconds. Finally, he sees me and asks "Which print do you want?" I tell him I'd like the Deadpool one. While he signs it, I tell him that it's great he came to a convention in Oklahoma and hopefully more big names will make their way here. He says "Yeah," scoots the signed print to me and tells me it's $30. I paid him and said thanks while he just went back to looking at his phone. It's the only convention in Oklahoma that he's attended--probably because Wizard World made him--and if he treated everyone like that then he may as well not come back.