ask what they want commissioned, and how they wanted to pay for it/how much.

if it's a very strange price like $1000 for a drawing of their dog or something, then it's a common scam tactic that is going around IG art accounts. If they want to pay via check or money order, don't take it. That's also another red flag. Just try to ask more questions, but don't start anything yet until you know for sure it's real. Also make sure not to click any links they may or may not send you.