The only time anyone has tried to rip me off in Bansko was in a taxi - you need to agree a price upfront!! we didn't once and payed double the norm.... Other than that never any issues.
Had no problems there at all, been there for last 5 years.
Last time one restaurant that we normally use tried to charge 27 leva for garlic bread instead of 2.7 leva, but I think that was a genuine mistake. Some bars are dearer than others (Happy end maybe the dearest to drink in). Check your food / drink bills the same as you would in the UK.