Rob has basically covered what tests will be done: 2 to 3 slow pulls, then half-a-dozen or so fairly fast pulls, checking for excessive extra shots. Personally, I'm not really fussed if there's just an extra shot from ten or so trigger pulls, it's more to check for half-a-dozen or more shots from those same pulls. And those are rough figures, so don't be a clever sod and try to quote them back to me if your marker fires 15 shots from 10 trigger pulls!
In addition, we'll be using the bottle slap test to check for the really unsafe markers.
I know this all sounds rather heavy-handed and pedantic, but a walk-on is meant to be a fun day, not a world championship with fame, fortune and free Pot Noodles on the line. The Foxwood walk-on gets a fair number of novice players, players with low-range kit, occasional players, etc and none of them really want to be zippered by some wannabe loaded up with all the top gear, just so he feel like a winner. (Although shooting TL is funny, but don't tell him I said that)