I'm sure its fine as long as it has a full history - but personally I wouldnt buy it.
About 3 months ago i bougght a 99 Fizzer with 19k on the clock, full history, recent service, 11 months mot and tax, new tyres chain and sprockets for £1,100.
Bikes are still really a leisure toy compared to cars and not a lot of people can afford to run both... meaning there are loads going at a decent rate.
Take a look on bike trader, ebay, gumtree, preloved, there's loads to be had.