wit this idea i think it would be a good idea to have each city have their own credit marketplace thus allowing for more trading of credits and the credit marketplace may become like the drug market where the prices change from city to city depending on the need for credits in that city (im not suggesting server priced credits) so someone could potentially begin credit trafficking city to city

not only would this make players travel more it would also allow for a more interactive credit buying system as opposed to just one general "black market" so to speak

Credits, when bought with real money, are what support the game and keep it alive. Are you suggesting that the game spawns credits without people putting real money into it? I think it would create a sort of inflation or deflation (I'm not good with Economy terms) and maybe people will be less motivated to buy credits-.

im not suggesting that instead of one general marketplace it be broken down per city