Going to echo the replies so far, even if it's not cleared stated in a TOS, the artist can sell printed copies of the artwork they do on commission.

Personally I will always ask commissioners first before selling prints, or arrange for a print to be given for free to the buyer in exchange for allowing me to sell copies. But this is not something that one should expect from any artists unless you plan to pony up a lot of cash for printing rights to be kept with the buyer.