interview at the gym

It will be based on lots of cold calling leads, showing people around who come into the gym and generally trying to see as many memberships as poss.

Just make out that you have no problems cold calling and i am sure you will get the job.

I would suggest googling Miller Heiman or Hieman (I forget which)

I although not directly in sales, have attended some of there teaching courses and conferences, read up on the information they have on there website and use it to help answer questions during the interview.

Also remember body language and wording when you speak to them.
Remember a sentance spoken with one choice of words can come across completely different when another set is used.