If you're going to sell it on ebay or gumtree or similar, I'd strip it of thumbies, F & R mechs and fit cheap Shimano stuff. It should sell for about £40 and you'll make a fair bit selling the gear stuff separately.
Alternatively strip brakes, chainset, wheels, frame etc. and sell all the parts if you really want to max your money. They all look in great condition, and there'll be buyers on this site. It would take a bit more effort though.
Also I don't see why people would worry about paying £100 when you bought it for £50, if they consider it a fair price. Nowt wrong with a profit.