We didn't buy a boat through Whilton so can't help you on that front, but we did visit them on quite a few occasions when we were boathunting. Even if you don't find what you want there you'll get a good idea of all the different layouts and what's available for the money you can afford.
I was astonished by the number of boats there that were very poorly presented - dirty interiors, cluttered, dirty dishes in the sink, that sort of thing.
I did find they were overpriced, but then you can always make an offer if you find anything you like.
We bought our boat last October from Harrals at Northwich who have a good stock of boats, most of them out of the water so you can inspect the hull as well. We have no complaints about the service.
Good luck, take your time to find exactly what you want and don't be afraid to bargain - I believe it's still a buyers market