I think in general you will find somethings stay true:
1) the older a game becomes, the more epic pokemon enter the game -> the value will go down because more options.
Example -> Charmander ... Years ago I saw auctions for 5m+ for regular epics. Now I just see a godly go for 1-2m.
2) Your popularity online will affect your auction. For example if some popular people auction an epic it will sell for 10m / 20m / 30m + but its not perfect. But if me or you auction a godly it will sell for 1-3m because not enough people will see the post.
3) Coordinating on forums is very hard and risky, I don't think you will find people doing that effectively, it's easy for someone like me to ruin a coordinated event, and getting caught will risk losing your account which isn't worth the small increase. I find it's probably not as common on real auctions, plus you will usually see 5-10 players on a real auction showing there is real interest. I doubt anyone is controlling an auction with 5-10 people. If they're trying to inflate prices I'm sure trade mods can trace the money and actively are.
Solution:
I think the REAL problem is the current market everyone offers to sell a pokemon and just says "offer?" this is so bad because it's a waste of time. Just list a price, serious buyers will ask for any price adjustments. Asking for Offer's is just a polite way of trying to scam someone to pay more. The only time "offers" is okay is for really pricey pokemon 5m+ because it's difficult to get an accurate price, but for epic mons I believe that has ruined the trade community and leads to wasting time.
As for as listing for bids, I have seen plenty of people who just post a pokemon for sale and ask them to message them with an offer, I don't see why that's against the rules but If I am wrong I will gladly edit this post