There have been bad reports on here about GSF, warnings about buying on ebay so the question that I really need answering is who makes good quality aftermarket parts?[/font][/size][/color]
GSF own brand parts are usually rubbish, as are QH, but if they're selling brands like Sachs, Boge, Pagid, Bosch, Valeo, LuK etc. you should be good, looking on carparts4less.co.uk I can see a tensioner for your car price at £43.80 made by INA which owns LuK, I'd suggest this is potentially a good replacement part but you'll need to double check on quality. If you want to get extra money from from that site one thing to try is put the item in your basket and then go all the way to checkout after creating an account and giving them your email address and signing up for any mailshots they do, then abandon your basket at the last minute and don't purchase, it sometimes yields a voucher within 24 hours
I always find that if you see if the company or group are an OEM supplier for any car brands that usually the cheap and nasty parts manufacturers won't be a supplier to any major manufacturer and that's a good sign that the parts will not be good quality.