However, where the results might be very dependent on the partnering equipment and listener preference I think anyone would be mad to buy blind via mail order. This is especially so where a product is in wide distribution (Richer, Superfi, Hyperfi etc) and heavily discounted both mail order and over the counter.
The cost of insured carriage for a return will eat at least £20-£30, then there's the hassle of cancelling the order in writing, arranging the courier, finding the depot or taking a day off work for the collection.... It's just a huge PITA for what is a sub £250 stereo amp.
If you have to take a day off and you live within 45 minutes of a major UK city then do it for something productive. Line up a few dems on a midweek day when the retailers will be quieter. Go take your headphones and listen to the Yam and a few likely contenders. In that price section of the market you also have Onkyo, Marantz, Denon, Pioneer, Teac, NAD, Harman Kardon and even Arcam if you stretch the budget a bit. Listen and buy and take home the same day. Beats mail ordering hands down IMO and you'll have some fun too.