[slipnkit]

Try to add variable like bool:OnMission[MAX_PLAYERS] = false; on top of your script.

Then on command change it to true.

Then it will be, if(OnMission[playerid] == true) SetVehicleParamsForPlayer(car_dealer_car[0],i,1,0);

Also what I think is, that continue; just finish "for", and not setting vehicle params.