OK, speaking as a hobby-inclined adult who is recently out of college himself (late bloomer), tell your mom that I am qualified to offer this advice:
Call the guy and arrange a pick up for the 40 gallon bowfront. Don't wait until finals are over; it won't be there. Heck, I'm broke, but if this was in my neighborhood you might have some serious competition. ;-)
Tell her that if the tank is in good condition, it will sell very soon. If you can at least get the tank in your door,promise her that
you won't worry about any other seahorse crap until AFTER finals are over. Then make good on that promise.
When you go to get the tank, look over it VERY carefully. Ask him if it has any leak conditions. Take a close look at the glass and make sure it's not too scratched. Take a closer look at the silicone seals and make sure they all look clean. You may see some small frayed edges on the silicone; this won't be a problem. Any large frayed edges, or obvious deep rips in the silicone - don't buy it. Don't be afraid if you see small chips in the glass edges, but if the glass edge has a chip larger than 1/8th to 1/4 inch, don't get it. Look at the seals on the front of the tank the most. Just so you know, Bowfronts are beautiful but have been known to develop leaks faster than regular tanks. You also want to look at the plastic frame - a 40 gallon bowfront should definitely have a crossbrace from the back of the tank to the front. Make sure this is still firm, and doesn't look or feel discolored or brittle. Some discoloration is acceptable, but if it's really bleached it will also be brittle - you'll be able to tell. Finally look at the bottom glass and check for the silicone seals and any possible cracks.
I would ask after the bowfront, the 40g long, and the 20g long. But that's just me - I'm not a hexagon fan.