I knew a friend that delaying the checks purposely. And he never get caught for delaying all his DC6 c-checks.
My plan to run a DC-10-10 without scheduled A/B-Checks and do them manually was not this successful. But McDonald Douglas was very happy to get a three month old aircraft back to perform a check from 30% condition to 100% for only $600k!
[Edit: Also I didn't know there is an extra section on the aircraft-screen: "Aircraft with very bad condition." I discover every day new cool things in AWS!
However, I think (and I think sami has said this onetime (s.th. like "the more times you miss the checks, the higher gets the chance to be caught", but I'm not 100% sure) you can delay the checks in different times. I once (in my very first beginner game) got fined for forgetting A/B-Checks. Mainly they must be done every week, so you forget it and it runs two or three weeks, you are very fast over this time.
C-Checks must be done yearly, so it's not this big deal if you delay them up to 1 month (this was my personal deathline with DC-6) while you can delay a D-Check up to 3 month (my personal deathline).
So every time you pass the "FAA-ingame-script check", the chance they will catch you increases.
By the way, I stopped doing this as I had enough money. I don't know what exactly your plans are, my friend, but I think you now have enough money for those checks too