I’m going to give this a pretty hypocritical answer because I’m behind on a couple commissions thanks to some mental health problems (though the two customers are aware of this and have been very patient, bless them in a very non-southern sense), but honestly– the artist should have been keeping you up-to-date from the start?
Things like pose and expression are able to be fixed in the preliminary sketch. Did they just crank out rough-to-finished without keeping you in the loop and getting your input? I wouldn’t consider myself the most communicative, but (in the case of half+full bodies) I’ll always send a rough sketch, lineart, and preliminary final to make sure it’s everything the commissioner wanted– if it’s not what they like after I show them three separate WIPs, then it’s kind of on them for not saying “hey, I don’t like that expression”, you know?
So if they didn’t give you that measure for what sounds like a full-body piece, then I think you have every right to say, “Look, I appreciate the effort, but this isn’t what I asked for.” It’s their mistake for putting all that effort into the wrong thing. If I’m at work and have to put together a new shelf of product and wind up putting together the completely wrong aisle, all that effort isn’t going to let me off the hook because the job I was supposed to do still hasn’t been done.
So yeah. Don’t be like super aggressive about it but do point out that it’s not what you wanted. It’ll be okay.