There are really only two rules when it comes to proper attire for a home closing: 1) Boston real estate broker and other professionals (lawyer) should wear formal business attire (sorry, no “business casual”); 2) clients can wear whatever they want.
Which I guess means there’s only one rule.
For men, at least, “business attire” translates into business slacks and shirt (my usual uniform), if not a sport coat and tie, or even suit(!).
P.S – Because of the pandemic don’t be surprised if your Boston real estate broker is not at the closing, the newest trend is to keep as few people as possible at the closing table.