Yeah, sharks are difficult to anthropomorphise. The biggest issue I usually find is that they have no neck. You either have to give them one, which often makes them look kinda not like a shark at all, or bend their heads over awkwardly at the gills, resulting in a hunched back that looks decidedly inelegant. Most furry artists I've seen that draw sharks take the first route.
There's a nice compromise between these two approaches in the picture here: