enigma1 - 12:04 pm on Aug 18, 2009 (gmt 0)

Well you maybe the admin of the domain but who paid for the domain in the first place? If the client was paying you should had transfered the domain to them in the first place.

Now if they didn't pay for the domain registration then you are the owner of the domain and do whatever you want. Sell it to someone else, charge them as much as you want for the transfer and the like.

From your posts it is not clear if you or the client paid for the domain and what receipts each one holds. If they did pay and possess the receipts (you were merely a reseller), they can get it back for sure through legal means and you can be in trouble for not transferring the domain from the beginning.