Mazuma are absolutely EXCELLENT. Have sold quite a few things to them and they are super speedy.
If you registered the item on Monday, you'd get the packaging on Tuesday. Send off the device the same day and they'll have the money in your account on the Wednesday. Never had an issue with them at all. Great company.
Some people do offer a bit more money, but i've heard a lot of hassles with them. Would rather get a little bit less and have an excellent service.