The estimate on monthly payments you were shown was based on an assumed monthly mortgage rate plus taxes and insurance. BUT .. they underestimated the cost of taxes which would average about $113 per month plus the principal and interest of about $177 per month ... IF you only had to pay the 3.55% they estimated after putting a down payment of about $10,000 and only borrowing $339,200.
So the monthly payment would be higher than what was shown as principal, interest, taxes and insurance even at that low interest rate as it would be a little over $300 per month. AND as the other agent told you, the HOA fees would be an annual payment of $1,680 in addition to that monthly payment estimated if you paid list price and put down about $10,000.
BUT ... also ... as the other agent said ... this short sale is under a pending lender approval contract.
And if you want our help in your search .. you can reach out to us a WatsonTeam@Gmail.com or call us at 404-932-7305 and we would identify and show you all properties that meet your search criteria.