[Dire]

The river is incredibly marginal. Hero likely has a crappy image due his style, he played the hand poorly and now has an incredibly difficult decision. IMO, there is not enough information to make an even remotely reasonable decision. This would depend so heavily on history, bet timing, game flow, blah..

And trying to give a range for villain here is just silly. Villain is bluffing or has hero crushed. There's no telling if he decided to float the flop planning to bluff a later street but was scared by the ace, if he's turning a marginal made hand into a bluff or what. Obviously his 'crushing' range is extremely miniscule, but what's important is his bluffing frequency and how likely hero's image/play is likely to have induced a bluff.

I think the comment: "you played it so weak up to now, so you have to call" is extremely legit. Hero's play and image could easily induce bluffs. Of course, there's no way of being even remotely certain. Not enough information. That said, I do think the weak play could easily induce a bluff so I would call this.