Whoever tuned it though, before blaming them, get a diagnostic log carried out. Especially if stock figures were suspect.
Agreed. However given that the OP's first post in this thread was edited by a moderator (see the reason), there must be a good reason for it.
The lower bhp figures in the first instance could be r/r lottery or perhaps just that the car needed a good service. Again, a good tuner would have checked the car for faults and if some existed, told the customer that they could not tune the car because of x,y or z.
If the tuner is reputable, then there should be no
problem with a refund or similar if the product does not do all it is supposed to, and cause adverse effects. I know Revo have a money back guarantee on their code for example, no questions asked. They will reflash the car back to stock as well.
If the MPG got worse after mapping, then it may be timing/fuelling issue in the software
True, but most people will see lower mpg when first mapped as they are much more inclined to give it some to see the difference the code has made
Another good reason to log it to see whats happening though