I can't understand how someone (especially someone who created the class) would "just forget" about a shift or schedule change.

Now, if there was an emergency or illness that'd be another story but it seems that the person just plain forgot.

Word of mouth spreads quickly and you can bet that these customers won't have very good things to say (which, unfortunately, will also reflect upon the company and the other trainer's abilities). I think damage control (personal apologies from the trainer AND store manager) is in order and it also might be nice if the company would throw in a coupon for ______ (x-amount off a purchase, free grooming session, whatever).

As for disciplinary action... I'm undecided. My first instinct is that, no matter how likeable, the person is dispensible; they've cost the company money and there's another to take over the classes until someone else can be hired/trained. But, past track record needs to be taken into account. So perhaps a demotion is in order. (Once word is out, will others sign up to take classes from this person?)

It's a yucky situation for all involved.