We just had a medium sized rainstorm and when I went out to the garage I noticed water leaking at least two feet inside the entire perimeter of the garage (only about 1/4" deep). 

Basement or foundation look for leaks, cracks that show signs of foundation issues.End of the day, apartments are a business, people buy them for the cash flow.

Default tenant that owes several months back rent has finally moved out and my mom who is the new new owner (brother died and left house and assumable mortgage to her in his will) is trying to get gas service but the gas company says service is still active and past due balance under tenant's name.What is the best resolution?

Plumber took a look and suggested it would be a good time to switch over to gas forced air furnace.

Heres a kitchen that had a slab leak at some point.  

It's an easy, free (except for gas) way to get leads. 

Values ranged from $110K to $125K.My had more SQFT than the $110K comp, I had a complete renovation, including a brand new Carrier HVAC with gas furnace, roof, etc.

What about when the roof leaks in a big storm?

Is it due to leaking?

Self-installed windows are likely to be leaking (even if it's not visible), as are the boarded-up windows and doors.