Han refers to Jabba as Greedo's boss. (As in Greedo is a regular employee of the Hutt.) Jabba even expresses a little regret that he's dead in the docking bay scene restored to the SE. (Crappy CGI and gratuitous Boba cameo aside, it's still the original dialog.) You'd think he'd be relieved he didn't have to pay him!

Greedo offers to forget seeing Solo if he coughs up the money on the spot. The line about "looking forward to this for a long time" implies a personal dislike or grudge against Solo. It may be splitting hairs, but Greedo does not come off as a professional bounty hunter, more of an opportunist who happened to spot Han in the cantina that day, and didn't live long enough to regret it.