Legally I think its 30 days but don't take that as gospel. Since its only been 10 days I think you're jumping the gun a bit, a lot of people work all the time and can only get to the post office on a Saturday.
You only need to offer a refund on software if it is faulty in some way - otherwise you're under no obligation. It may be that the software is faulty - you don't say, other than that your customer told you it was 'no good'.
Like all things,errors can occure. I purchase quite a number of items via ebay, and on occassions I have had the 'no good' software, usually I have found the problem as been through the way I have tried the programme out. I would suggest that a simple have you installed it this way email, may bring a better response.
Ebay have a very good community forum, and any questions or answers are usually given a very quick reply by other people who have had similar experiences. Give that a try.
Would also suggest that software can be copied, so be a little wary on this point. Nothing like supplying someone else at your expense, if you see what I mean.Have they given you a feedback yet!.
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