The sellers feedback looks OK, he/she has sold a few of the before at the same price, all with +ve feedback. Most of the feedback is for similar value electronics / photo gear so there is a pertinent track record. Might be worth asking the seller f they are new or shop returns, what is the warranty, and why so cheap?
The only thing I'd be wary of is that payment is requested by cheque or balance transfer and NOT PayPal, so a refund could be tough. The amp is from 2009 so is a year old, it may be bankrupt stock, hence the price.