The main problem is we mainly know what their money making method was: Cacti, Melon and Egg Profit Shops, Block Shops and an Overpriced book shop for the first 5 Days (Like 10+ Islands are doing) before we spotted things that did not add up.
The luck required to obtain 32 IGS, 23 Creeper, and 17 Magma from Crates are astronomically low. Also to mention that we've only seen them buy crate keys on 3 Separate Occasions (None of which are big amounts like 30+ Keys). Although the strange part the most likely method of them getting their Spawners were Crate Keys.
Not to mention: A solo player grinding Cows nonstop can only make $1,15mil Per Hour AT MOST. So assuming they'd grinded all of those spawners and bought all their spawners for 2/3 of the original price. It'd taken that one player about 9 DAYS OF NONSTOP GRINDING to get all of those spawners listed (400+ Cow, 23 Creeper, 32 IGS, etc.) Yes they all have teammates but if they all grinded for all those spawners it'd still taken them about 25 Hours Per Player to get the money required to buy all of them (Assuming they next to never did IRLs, which are only worth about 100k per USD, or 5 Minutes per USD)
EDIT 1:
Good point, some of my "Tryhard" friends, for example Erik has been playing all this time about 8+ Hours a Day and keeps a close eye on /baltop and /is top, He also has never noticed any significant change in balance over the span of ALL OF HIS TEAMMATES. Which is severely odd.
This is is just he-said she-said, unless you have people monitoring their island 24/7, with an acutal graph on their gathered wealth and playtime, then this is still just a hit in the dark. You would need to have a literal record of at least a few days, to account for playtime, balance, island levels, and any activities they carry out in-game, trades, sales, items they've purchased, vote crates, purchases etc., and like I mentioned earlier, there could be players cooped helping or giving their daily rewards to them. There are hardcore grinders and it seems pretty to say it's duping.
But, again, like I said before, if they're duping I'm sure our attentive and caring staff will handle it swiftly!