I've just seen one on ebay that I like the look of, ridiculously cheap for what it is but I don't exactly need it so trying to be good and resist!
If they're online and a proper business, under distance selling regulations you have up to 7 days to inform them that the product is not suitable and to return it as new for a full refund
If it's a private seller on ebay or whatever tho, you may just have to try your chances! If it's cheap, maybe you could always re-sell it if it doesn't fit?