or coinbase, it's probably the easiest way to convert btc to fiat for a merchant
He wants to accept coins first and as J603 said there are some problems like "double spend".
The easiest way is to have people use their smartphones and scan a QR code, and then send the payment that way. Of course, you have to either trust that they're actually sending it and let them purchase their good or service instantly, or have them sit around for 30 minutes while the transaction gets confirmations.
However if "double spend" is not a big problem for you then there are many ways.