This is exactly what I was getting at in the other thread. It all comes down to intent. If doing anything to get a lower average in order to gain somewhere else (handicap tournament), then it is clearly sandbagging.
I have no problem with people throwing urethane and/or plastic if that's also what they use at these tournaments. Or if they have another league where they establish a truer average throwing resin. Challenging yourself is one thing, but to then go with the easier route in order to cash down the line - using that lower average, that is downright sandbagging and wrong.
Personally, I do not even complain about these people. I still go out and bowl, knowing full well that odds are against me. Same with bowling scratch events against better bowlers. I like the challenge. For me, bowling is not about making money. At the same time, if brought up in discussion, I'm only going to tell it like it is.
Sandbagging is all about intent. Unfortunately, this intent is often hard to prove.