Are there different fences giving different prices for loot in the city?

I just started playing Thief: Deadly Shadows. I'm now in the city for the first time.

I'm wondering if there will be different fences over the course of the game. Will they give different prices for my loot? Does it make sense to hold back on selling now, to get better prices later on?

If not, is there any reason not to always use "sell all"?

No, there are no price differences between the fences, however some fences will only buy set items (jeweler only will buy gems, etc).

As to holding on to loot for selling later, there is no real point, because there will be no change in selling price later in the game, and thus there is nothing to gain from holding on to loot.