I'll put myself on the line and present a possible sandbagger scenario. Let me know what you think. I had only been playing recreationally for a little over a year but alot at my local course. My first year in PDGA at my 3rd event I won in MA2 at my local course, shooting a 983avg with the 3rd best overall score (-5 & even, 2rds). During my first year in PDGA I played alot of town events, however my rating never got above 934, as I didn't play well out of town. My second year in PDGA I only played about 3 events and then took 6 months off completely from disc golf.
At the start of my third year, I wasn't sure if I was ready to play MA1 permanently, so I started out in MA2. I finished 3rd in the first event, shooting alright (945avg). The second event was at my local course, same event that I won two years ago. I was debating whether or not I should play MA1 or MA2. I've played both divisions previously at other events, mostly in MA2, and my rating was still around 928. So I decided to play MA2 hoping to do well and use it to spring into MA1 for good. I ended up winning MA2 only by 1 stroke, and it happened on the last hole (967 avg). I did get the bagger calls from the local crowd, but I knew then that it was time for me to take the step up to MA1. Since then I've played nothing but MA1 and my rating has bumped up (941), and I have been averaging 950 this year.
Personally I think sandbagger calls come from locals where a player has a higher advantage and does well at the local course. In my scenario I did well at my local course but out of town I struggled and was inconsistent. My rating dictated I could play MA2. Looking back, I could see that maybe local players should consider playing a division up, espicially if they have already won previously. So it was an awkward position I was in, but I don't regret it, and my thought is that you play within the division you're rated in, until you you're ready to take the next step up or your rating dictates as such. I didn't mind the sandbagger calling, it actually gave me a boost of confidence and I wouldn't of done anything differently.
The sandbaggers we should be looking out for is someone who intentionally throws their game to get a lower rating to stay within a certain division. Or a player who plays local leagues where PDGA ratings do not define which division a player should play in thus allowing them to play in lower divisions.