I have cashiers check prices all the time. As long as I tell them up front it's just a price check, there hasn't been a problem.
Managers and CSR's at that little podium near the registers can also look up prices, but it's a longer procedure, so they may resist.
For anyone living near San Marcos, TX, I hit the Sam's on Wonderworld during a road trip. Saw some decent prices like Ghostbusters for $15. There were several other decent titles for $18 and up, but I was in a big hurry and don't remember exact names. My bad.
They killed me because they had Prototype for $12, but when I tried to buy it for my brother as a gift---DENIED! They were sold out. What a bummer.