O.K so here are 10 ways you can save GP on Combat Arms...
1. Buy Guns for 1 Day instead of 7 days because it will motivate you to squeeze every last use out of that weapon.
Note: 1 Day Buys are Exactly 24 Hours. Most-likely, you can use a Gun for 2 Days if you play at a normal time.
2. I recommend getting used to the default gun, incase you get stuck with it.
3. If you aren't owning in Elimination, Search and Destroy might be for you.
Search and Destroy gives amazing rewards, if you win.
4. Try to master every weapon, incase you ever have to use it.
5. Modifications aren't worth it if you have low GP.
Instead, save it towards another 1-Day Gun.
6. If you suck at using your Default Weapon, try Knife Only Battles.
Knife Only Battles might be better, as your knife doesn't suck that much.
7. Before buying a weapon, test it out.
Play a regular map with your default weapon and pick some guns up (E) and test them out. Try to find the gun you can get the most kills with, and buy that gun.
It isn't worth losing any GP.
8. The G36E can be a great buy, as it's scope is better than any sniper scope (range-wise)
9. Don't be hesitative to go to the winning team. The winning team will have better rewards, and help you get more GP. If anyone calls you a noob for doing that, they just have too much pride to change teams.
10. Try to make profit in the 2 days. What is profit you ask?
Profit is when you gain more than you spent.
For example, you buy a 1 Day Gun for 900GP
You made 1000GP. Then you made a 100GP Profit!
100GP Profit sounds little, but it adds up!