The Marshall Tavern is once again for sale: owners Daniel Altman and Avi Atid put it on the market within the last week, at a price of $550,000. That’s not much more than they bought it for in 2004, when they paid $512,000 for the property, which they planned to renovate and turn into a five-unit bed and breakfast. Mr. Altman, an architect on the cusp of his 80th birthday, said this week that he…