Sandbaggers often beat themselves when the chips are down and I find that extremely funny!
I was trying to read an opponent's level at a local watering hole. It was just a casual game and I wasn't out for blood or anything, the only thing I had to lose was quarters for table time. Well, I was kind of cruising along, in sandbag mode, and he just gave me a whipping. By the time I realized this guy was a threat, I couldn't switch gears fast enough to win the race. I got a laugh at myself for what I had let happen. I guess it would be better to watch them play from the sidelines to figure their level. Once you're at the table with them, you gotta stomp the gas if you have to win. Sometimes it can be a fun challenge to "just" beat someone at the table, but why play headgames with yourself if you're not trying to hustle someone out of a few bucks? I had been reading books about road players who would try to lure some suckers in and rob them. I wasn't trying to rob anybody so why play games? My head wasn't right and had found a "fun" way of playing pretend to amuse myself and lost the game.
I would never sandbag on a league or tournament setting. I'm there to do my best and improve myself. So what if I go up a level and have to play harder to win? We play for a challenge don't we? As long as I keep focus, my mind isn't the weak spot in my game. I can adapt to any challenge on the table mentally, but I'm still working on getting the rest of my body to the point it can keep up with my head. Forcing my body to do tougher things only helps. I've never seen a body builder who only uses 5# dumbbells. They push themselves to the breaking point and it only improves their muscles.
Sandbagging hurts yourself because it never puts you into a situation where you have to really bear down to win. Trying to cheat the system for an advantage and play handicapping lawyer is just mental masturbation. They don't have their mind developed and in the right place to actually want the thrill of winning. They are scared of winning by simply playing their best, so they try to stack the deck in their favor so they can still win at a subpar personal level of play. Not me, I want to play better players and pull myself up from a bloody heap on the floor and still win. Sure I might still lose but hopefully the other guy is at least winded.
Do I still lose? Of course I do! But losing while being fully lucid at the table and playing to win will teach you more than thinking you lost due to sandbagging or bad rolls, etc. Own your own mind and game at the table. If it disappoints you, that's the first step to becoming a real player. You can't be in denial, you gotta accept that and jump into the forge. No piece of metal became steel without taking a beating from the blacksmith's hammer first.
Blaming sandbagging opponents for a loss is as stupid as saying you lost because of bad luck. Bad luck is between your ears, not on the cloth. Develop some mental toughness and welcome the heat of the forge and the hammer, you're gonna end up much stronger that way. Excuses are just the first sign that you enjoy and want to be a loser. Own it and get to work.