If you are able to complete the game in professional difficulty you will unlock all the secondary and special weapons. Pro difficulty is unlocked after you have completed the game in either recruit or contractor difficulty

After you have completed the game in either recruit or contractor difficulty all primary weapons will become unlocked when you play through the game again. It also unlocks the professional difficulty mode.

To unlock this mode you just have to complete the game once on either recruit or contractor difficulty.

There is a little trick with which you can accumulate quite a bit of cash, you just have to be prepared to do the same thing over and over again... Ok, here is the deal.

In China, complete the taasks at the beginning of the level, blow up the bridge and get to the hovercraft. Here the game will auto save your money. Now quit out of the game, reload and go back and do it again... And again... And again... Well as many times as you want.

Complete the tasks to get the corresponding GamerScore.

Boots on the Ground - GamerScore 10:
Complete a versus ranked match.

Weapon Specialist - GamerScore 15.
Purchase 3 weapons.

Out of Debt - GamerScore 15:
Heal your partner for the first time (training doesn't count).

The Devil's in the Details - GamerScore 20:
In a ranked match complete 20 minor objectives.

Fission Mailed - GamerScore 20:
Kill 25 Martyrs by shooting the Bomb Packs on their chests.

Flip You. Flip You For Real - GamerScore 20:
Using the Melee Attack kill at least 50 enemies.

This is my Boom Stick! - GamerScore 20:
Using Shotguns kill at least 250 enemies.

Spray and Pray - GamerScore 20:
Using Machine Guns kill at least 250 enemies.

One Shot, One Kill - GamerScore 20.
Using Sniper Rifles kill at least 100 enemies.

Alright, Who Wants Some? - GamerScore 20:
Using SMGs kill at least 250 enemies.

Beast with Two Fronts - GamerScore 20:
In Back-to-Back kill at least 50 enemies.

Big Boom! Big Bada Boom! - GamerScore 20.
Using RPGs kill at least 25 enemies.

Dead Man's Hand - GamerScore 20:
Using Handguns kill at least 150 enemies.

Seven-six-two Millimeter - GamerScore 20.
Using Assault Rifles kill at least 250 enemies.

Surviving The Game - GamerScore 25:
Complete a ranked match without ever needing to be revived.

If It Bleeds, We Can Kill It - GamerScore 30:
Kill 25 Heavy Armor enemies.

L'Abattoir - GamerScore 30:
In the Power mode of Overkill kill 100 enemies.

Running Man - GamerScore 30:
In the Stealth mode of Overkill Kill 75 enemies.

Starting a Riot - GamerScore 30:
In Co-op Riot Shield kill 50 enemies total.

Stonewall - GamerScore 30:
Using the Riot Shield melee attack Kill 30 enemies.

Field Medic - GamerScore 30:
Drag and heal your partner 25 times.

Two Eyes are Better Than One - GamerScore 35:
Using Co-op Snipe kill at least 5 enemies.

My Virtual Friend - GamerScore 35.
Using the Partner AI complete ALL missions.

One Gun is Enough - GamerScore 35:
Win a ranked match without buying any additional weapons.

Retirement Savings Plan - GamerScore 40:
In ranked matches earn one billion dollars in total.

My Kind of Case! - GamerScore 40:
Collect ALL of the information cases in the entire game.

If I Were a Rich Man - GamerScore 40:
Over the course of campaign mode earn one million dollars in total.

Say Hello to my Little Friends - GamerScore 45:
Purchase the DAO-X Protecta, MP7, M134, MGL MK-X and the M107 Light Fifty.

Fear is The Mind Killer - GamerScore 45.
Spend 1 minute straight at full Aggro.

Man of Many Masks - GamerScore 50.
Buy every mask variant.

Elite PMC - GamerScore 50:
As a Professional complete ALL missions.