A possibly GTS/Market System?

[i know a Marketplace system has already been planned, but I want to add some suggestions about how to go about doing it]

So I recently came across a game by the name of "Pokemon Planet Online" It isn't a very popular game at all, it's a browser based game, and has only been around since late last year I believe. (I wouldn't recommend playing it, the game is quite broken and it's not very fun to play at all) However, they had this market system implemented where players could put their Pokemon on a global market for a certain amount of cash.

The only flaw the system had was the fact that you could access the Market from as early as the first PC, so alt runners, they could pretty much just buy a high level Pokemon right off the bat with transferred currency from their main. But that could easily be fixed by perhaps making the market accessible after beating the E4 and/or seven islands.

So here are my suggestions to include in the system, to possibly make a better version:

-Only accessible after E4/Seven Islands - (to avoid people buying high level Pokes early)

-Having a certain price cap for each Pokemon to avoid overpricing - (to avoid ridiculous over pricing - Possibly no price cap for Shiny alterations)

-Having a cap for the amount of Pokemon people can sell at 1-3 - (to avoid flooding the Marketplace)

[PS, I have no idea of how the current Marketplace system is planned to work, so if these ideas have already been implemented, please excuse this post]

Any thoughts?

-Purple