If desperate for cash a very dangerous tactic to hold on hoping for a price rise which may not happen. Collusion between jobbers does not happen They are trading numerous stocks and in any event Fly be much too small to bother with
Surely sales are either to raise money, settle outstanding positions etc if you are selling it is not to keep the price down, selling means those holdings no longer exist
There are no codes. Job beta compete with each other like bookies on a racecourse. Why would they collude? And in any event illegal and rules strictly enforced. Read a good book on how the exchange works as I note you are a tyro