Fruit machine - payouts

Just wondering whether anyone else has had a fruit machine make the wrong payout; and if so (I'm in the UK) how they got on.

I'm more worried not by the shortfall, but more whether the machine has been properly tested, and what else might be wrong. In this case two "wild" on a winline should have a payout of £1, but it only paid 50p. Being computer background, my assumption is they would at least test every possible simple win. Does it sound reasonable to see whether I can see their test plans or results?

The machine has to stay within a certain percentage payout and has regular feature games. So my guess is that the values of the features would, in theory, make up for any under or over payment - thus in the long term someone would win my underpayment. However once when paying a machine for 13p (it was near Halloween) one feature paid 78p even though all payouts were a multiple of 5p and I was told it pre-determined a multiplier win and spun the reels accordingly.

From what I understand here, the pay table listed cannot be wrong and if a casino posted the wrong pay table for a machine, they would have to pay it, but would act like they didn't or were doing you a favor.