When it comes to physical stores, the general rule is "location location location", and just based on having lived near Cambridge for a decade and spent most of my time there Inman Sq just feels like a suboptimal location for a bookstore.

This is assuming of course that a problem is getting more traffic. I don't know if that's an issue, or if the problem is the "conversion rate". It would be interesting to find out what's working and what isn't, but don't know if you're inclined to share further. Myself I'm not in a position to take over, but I sure can provide free advice :>

I've always dreamed of hybrid book store/coffee shops. Perhaps ones that sell subscription access, becoming for-pay lending libraries with a book inventory that adjusts to patron demands. That way you have recurring revenue off each customer, and you can hope people sign up for it like they do for gym memberships and then don't show :)