Like I said, if the owner isn't there..... then the owner isn't there. Probably is never there.
They don't work on commission... They're probably paid like 30 Baht per hour to sit there just so the store doesn't look empty. And they're probably teenagers who probably can't speak a single word of English. The type of excellent customer service you're expecting doesn't happen accidentally, or naturally. It takes an enormous effort and hard work to diligently maintain it. .....and many shop owner's simply don't. End of story.

Probably the owner is the wife of some rich guy.... and she couldn't be bothered with such "managerial" duties.

Oh, and also, I've *never* been asked, "Would you like to try that on?" Never in Thailand. Never in the USA. Never even at the Versace or Prada stores on 5th Ave. This isn't a 1955 movie. If you want to try something on, say, "Excuse me. Do you have a fitting room where I could try this on please?" That works every time.