When local PD finds out that your business is the "go to" place to trade in guns the ATF will be the least of your worries.
A Federal Firearms License is required for anyone engaging in the business of dealing in firearms. While the occassional trade is not going to be a problem, if you advertise the fact that you accept payment in guns you will no doubt attract the attention of ATF and law enforcement.
There is no way for a Texas gun dealer to verify that a firearm is not stolen. The Federal NCIC is strictly limited to law enforcement for official business.
Some states may allow access to their own database but NCIC is LE only.
Occassional trades shouldn't be an issue.
Advertising in the local paper "No cash? We take guns!" will get you in trouble real quick.