Local pickup for speakers - should I let the buyer in the house or use the the garage?

Very high probability that this is fine, but I'd try to find someone to be with you if, for no other reason, you'll be more comfortable in your interactions. I'm maybe a little cynical - was a federal prosecutor for several years-but the really talented bad guys can make you believe they won the Nobel Peace Prize and ended world hunger. I'd have someone with me. 

After you have talked to them on the phone and they seem ok, then look at what they drive up to your house in. if it’s an old beater, they look like they just got out of jail and they are buying thousands of dollars’ worth of gear maybe run,  if they drive up in a decent car/truck, dressed well etc, they are probably ok. I assume you have insurance. 

All of my customers drive a beater car, look like they have just gotten out of jail, and have a broken down meth still in the back seat. You don't need to always take cash, sometimes trade is fine.

Treat the buyer the same way you would want to be treated if you were him.  Remember, he thinks you might rob him.

Sus out the buyer as best you can and then go with your gut.