Alright. This is something every store can do..
A) go to a shop that has a console that you can play on (most places like eb games) and check its firmware.. if its what you want. make an offer or just ask how much is it. (normally cheaper.. score!!!)
or
B) ask at the counter when did you receive your oldest stock for the ps3. A manager should be able to confirm this with you. just ask for the oldest one

lol.
C) go to somewhere that trades in games and consoles..
eg.. cash converters, games trader, ect
You are allowed to ask "can I see this product in working action".. check out firmware.. normally the older fat ps3's that you find in them places normally havent been online in a fair time so theyll be low firmware