Pro tip: If you have no public restroom and the mere "yes or no" question is that offensive to you, put a sign up that says "no public restroom"

I realize it's probably a corrective / reactive measure due to vandalism or possibly drug use in the restroom, and maintenance costs add up even for the former (and a customer / employee finding someone passed out or worse from an OD definitely could be traumatic) and sometimes the middle ground of a "customer restroom only" is done instead.

In fact, upon the adult realization of that, I sometimes will buy a water bottle or snack or whatever from that type of store, both as a 'tip' as thanks to those who do have a public restroom, and so I don't have to get the runaround "Got a restroom? For customers only. Okay, hang on a moment (grabs item)" especially if there's a line. And then if the purchase was just to get into the restroom, if they have no public restroom, guess what? I put it back instead of buying it, because I haven't paid for it, but it's a sealed package or bottle whose seal I haven't broken, so there's no problem for others by putting it back.

If I'm looking for a restroom I look for signs saying they do or don't have one before even asking.

And then there's the ones where the restroom isn't open to the public, but I'm like the first guy of the day or the cashier clearly just started their shift - and I ask the yes or no question 'do you have a customer restroom' and they YELL that they don't have one. Like even appearing polite to other people in the store went out the window, when I asked a YES OR NO question. Sometimes they even deny service when I clearly intended to buy something. It's not like I had been there before, been told that and forgot. Honestly if I get an attitude from the person at the front desk when I'm holding something I clearly intended to buy, I'm probably just going to put it back. No sale for you.

If I were going to stuff the item in hand into my clothes in the restroom (shoplift) I'm hardly going to speak to the cashier, ask them to lead me to the restroom and then carry it in right in front of the cashier who gave me the key / opened the door. I might as well be wearing a sign that says 'shoplifter' and that's what the sales floor cameras are for (there can legally be a camera directly OUTSIDE the restroom door even, as long as it's not inside there) it's not like a store employee can tackle you, but they can darn well deny future re-entry.

Here's a thought, if it's that infuriating to answer a yes or no question even at the beginning of your shift when I was being pleasant about it, put a darn sign up that says 'no public restroom'. Not everyone reads the signs but at least you can point to it and have an excuse to scream bloody murder at a customer who was going to be polite, but is now probably going to not buy anything (even if you're still willing to serve them)