Assuming your relationship is purely on a professional basis, i.e. you are not personal friends, then you can change if you wish, and your trainer should be professional about it, in much the same way that hairdressers are. You are not obliged to use a service from any individual if it doesn't suit you, that is your perogative as a paying customer. If your trainer queries the change, which he or she may do to ensure that it's not a personal issue, then say something non-commital like 'I just fancied a change, thanks.', then smile, and walk away, and that should be the end of it. If your tainer mentions it to you again, this is being unprofessional, and you should mention it to his or her employers. Explain the circumstances, and say you regard the matter as closed, and don't want to deal with it again. That should be the end of the issue. If not, you are paying the wrong gym, and you should move - the option of telling the owners why is up to you, but it sounds like you;d be happier just walking away, although hopefully that won't be necessary. Don't worry, you are entitiled to your choice of trainer, putting up with things and saying nothing is a British disease, don't go along with it! Good luck.