This happened to me as well at Jellyrolls. The waitress would not open a tab and made us pay for all drinks individually. I tip once, at the end so I left the tip lines blank. When I looked at the charges later they were all 3 and 4 dollars MORE than they were supposed to be!
We had to call to get it corrected.
Please be vigilant. Very few WDW servers are going to scam you. Heck we've gone constantly for about 5 years (we're local) and it's only happened once. But just because you're in WDW that doesn't automatically make it safe.