Of course sandbagging is cheating.
I have been beat by net 59, and net 60 in our match play championship over the years at my club. Those are my worst experiences with sandbaggers.
I guess I don't mind too much, because I benefit from the more common occurrence which is vanity handicaps. I see lots of people who have a bad round and insist it not be posted. Also, those that shave strokes and post the result. Your loss my gain.
The handicap system in the US does have it's flaws in allowing social rounds to be posted. Most of my rounds may be social, but there is usually a bet, and being a stingy *******, I hate to lose money, so I think my handicap is fairly accurate. Most GCA competitions have me usually not holding my own until Buda last year where I did quite well. I had been struggling through most of the summer with my handicap going up, but was able to turn it around just before the trip.