You understand it exactly correctly. Also, I'm sending those transactions with 0.01 BTC (~$1.3) in fees, which is roughly half the $3 payment (after credit card processing fees).

The user can input whatever address they want, so technically they could use it to buy Bitcoins, but still - the amount is really tiny and insignificant, and it'll be highly non profitable ($3 for bitcoins worth ~$0.0000013).