I think it is a much more common practice with the Democrats in the inner-cities.
I’d use the word “liberal”.
I first heard about individuals selling or trading their votes during the 2000 election.
I know of a liberal acquaintance that traded his vote for a Nader vote on the internet. He didn’t even understand why I felt this was immoral, unscrupulous or wrong. He didn’t get it and I couldnt explain it to him.
As a conservative, I wouldn’t sell, trade or give up my vote.