Is this bad form?

[northernladuk]

Don't be fooled in to making a mistake just based on the rates other agencies are offering. It's highly likely they have inflated the rate just to get the better candidates first. People that do apply form the higher rates will find that this figure suddenly drops to the same or quite possibly less than you have accepted. IMO don't jeopardize a good thing based on the stupid games agents play.

[BolshieBastard]

You haven't even got the role yet. I would keep interviewing if I were you rather than worry about the rate you don't yet have.

This.

And what sort of model has an agency make a verbal offer to the OP yet still go to market via other agencies?

Absolute lunacy. If I was the OP, Id keep looking for a contract.