No I wasn't kidding.

I'm not saying someone may not want to replace a badly worn tire. But there's a wide gulf between recommending that a tire is replaced when it might still have some miles in it, and saying it's necessary. When I was in the retail bike biz almost a half a century ago, we often pointed out worn/near end of service life items. We'd tell them they might get by for a while, but would strongly suggest a replacement if they were planning a tour. A worn out tire flatting is a minor inconvenience, easily dealt with when in town, but a more serious issue far from home, so my don't leave town phrase wasn't accidental humor.

I ride light tubulars and my tires have less tread thickness when new than the tires most people throw out as worn too thin. I'll ride old tires until they die, but I'll often replace them before longer trips or multi-day tours. On my commuter, though no tire ever comes off until there's obviously less than 20 mile left in it.

Context also counts, If it were the chain alone or the tire alone, I doubt there'd be this thread, but the two together is too much.

The very existence of this thread, is evidence of the OPs distrust. Right wrong or otherwise, the trust issue is real, and one of the main reasons people leave bike shops. Just as great doctors can lose patients because of bad bedside manor, likewise otherwise good shops can sour relationships through impressions, as opposed to reality. It's not about how good a mechanic you are, but how much your customer trusts you.