You have to be joking??? Based on this handicap system, just make it a scratch league.
For all of those who want below 90%: The object of the league is to have competition. I see many statements on this site about achieving and making the shots when it counts. Yet you who chose this type of handicap want it easy. You don't want any team with a lower average to beat your team ever.
So you thinking is like this:
"I buy expensive equipment, practice every week, and this guy who just threw a 220 (160 average) wouldn't stand a chance against me in scratch. It must be a mistake. He has to be sandbagging. Anyone with a 160 average should NOT throw 60 pins over his average (Yet I carry a 210 average and have thrown numerous 270+ games in the year, but that is different). We need to have a league meeting and stop this"
You should be welcoming these bowlers into your league. Instead you call them cheats, when you lose to them. Your not helping getting new bowlers into this sport.
Why can't a guy with 160 average shoot a high 600 series? With the new equipment and on the THS, it makes pefect sense it can happen! We all have nights where throwing the ball was easy and we scored very high.
Nobody likes to lose. I always play to win, but when I lose I don't immediately think sandbagging. Its usually because of my lack of abilitiy (or my teams) that night. Yes there have been times that I have thrown 260+ and lose to someone who throws a low 200 game (140 average). Its part of the game.
We have all been in this sport long enough to tell the difference from a legit 160 average bowler and cheating 160 average bowler (who really has a 200+ average). You can tell.
When dealing with big money, there is no question the temptation to cheat is greater. Setting the percentage below 90% is not the answer. You need a committee to watch over this (Maybe its all team captains). It just can't be the officers. If you see someone (or a team) that seems to pour it on at the end every time or seem to miss spares at the end of a game when the lead is huge, then let them know they will be looked at.
You have to be upfront with this league policy. No team is exempt. It has to be a written complaint. The person writing the complaint must give detail information of the game or series bowled. Simply stating a team is cheating and leaving it to the committee figure it out is not good enough. If you get a enough complaints on a certain team, then that could be a red flag. Maybe just stating you league has a committee might be enough of a deterrent to keep the cheating teams out.
Of course that will probably never happen. Most that bowl leagues don't want to get involved.
Another idea is to make the oil pattern more difficult, but usually when that happens you lose bowlers. You got alot of league bowlers that will get upset about averaging 30 - 40 pins less.
The idea of setting a low average cap, isn't a bad idea. I would think anyone below 160 probably wouldn't want to join a big money league.