Thanks for all your help guys. So I guess in my example (which really was just a hypothetical example) I would have to figure out the value of the tv, let's say value was $5,000 USD. And he pays me 1BTC on March 9 when the price of BTC was $5,300 USD. So I guess my 'cost' basis would be $5,300. Then when I sell the BTC later on at $15,500 my capital gains would be $10,200 ($15,500-$5,300) and I would pay taxes on that.
Yes doing it like that should be safe. You should have a signed paper for the sale though, with the all important date so that the price of BTC can be checked in the future.
On another forum I'm a member of it's common to print a bill between members when trading stuff, it's a way to protect the buyer.