I found printme3duk.com very fair.
When a roll of filament didn't turn up they arranged for another to be sent after we'd given up on the courier.
The day they sent a replacement the courier turned up with the first so I emailed them to try and stop them sending another. Anyway I got a phone call back and they said that as I had been honest they'd let me have it for free!!!

If you ring them up they will often give you a better deal than the online price
I can recommend the filament as well so it's a good place for UK buyers.