I hate to say it, but after you've sent him the $50 and he pulled the "I'm sorry, but I just sold it. I got something that is worth more in stock"-trick on you, trying to gain even more coins from you,
didn't get at least a little suspicious?
1kvo38NsLZpTTGQxngpuFjJCtBnpX5fgF seems to be cloudbet.com deposit address
Another address that deposited into this is 1CvgpjjQoRb56qBVDWQYvnPsUwLUU5yHVn.
That address is mentioned in a scam accusation against
AllGoodsBTC also involving GiftCards
here.
It did get suspicious. I am not sure why I fell for that. I guess I am someone who have to fail a time or two before I learn.