Obviously you've already been to a court, and at sub 5k that was probably small claims.
My experience has been that the judge is unlikely to be an expert him/herself, and will be listening to both 'experts' on the basis of what an ordinary person would take from the advice/services/products promised vs what was delivered.
If the claimant has acted reasonably in the judge's view, and the defendant has acted unreasonably, then the appeal will probably fail. My unqualified approach to small claims court cases has always been to try and show that what I have done as a claimant has been what any reasonable person would do, with a broad set of criteria rather than one single showstopper. I then try to demonstrate that the defendant has done or omitted to do things which would have given me an opportunity to avoid whatever I am claiming about, or not buy the service or whatever, i.e. not losing the money I paid.
A showstopper is great to have, but you need a backup showing a generally distasteful set of actions by the defendant. That way you can obtain the benefit of the doubt when the judge makes his decision.
BW