We are probably getting quite legalistic, but if I was said owner and had similar motivations....
1. Sign saying consent to pat search.
2. If weapon other than firearm was found, I would reserve the right to refuse service if I so desired. I might allow, for example, a folding knife of a certain length, but not a sheath knife of the same length (even if both were legal, per State law and/or city ordinance). Things like brass knuckles, stun guns, and the like I would refuse service to.
3. If the customer declared a firearm, I would do as local law enforcement does, and ask for its location and a presentation of the CHL. Remember that "concealed" and "hidden" are two different things. If the customer did not have a CHL, I would refuse service. If I asked for declaration of a firearm, and the customer did not declare, and I found one, he would be booted regardless of CHL status.
4. I would post no signs stating no right of entry for firearms (30.06 of Penal Code in Texas), but I would make it clear in English and Spanish (a State requirement) that certain rules applied for right of entry into my establishment, and that I retained to right to refuse service at any time.
And I would quickly go out of business.