Easy Cash and XP...
	Various Steam Achievements...

At various points throughout the campaign, you can buy items cheaply and sell them for substantial profit and experience. An example of this technique can be found in Henderson, where a doctor sells medical supplies. Once you have the option to purchase bleach, make sure that you buy as much of it as you can afford. To the southeast, you'll find the makeshift hospital, where you rescue Nina. After doing so, head back to the hospital, where she will offer an ongoing quest. The bleach that you previously bought for $168 can now be turned in for around $1200-$2100, with an accompanying reward of around 14,000-55,000 experience. You can repeat this process as often as you like.

Achievement	How to unlock
Achiever	Finish all quests in the game.
At Your Service	Rescue 20 NPCs from clench.
Better than the arm	Kill 25 zombies with a chainsaw.
BrainLess	Kill 50 zombies by smashing, decapitating or shooting them in the head.
Breaching the Tunnels	Successfuly defend the tunnels entrance.
Bully	Kill 100 zombies with a kick.
Combat on the roof	Survive the horde on the roof.
Deafeat Harlow	Deafeat Harlow.
Dream Team	Complete all the main quests cooperatively with any number of partners.
First Do No Harm	Finish quests for Cecil in hospital.
Gain level 50	Gain level 50.
Gain level 70	Gain level 70.
Heart of Darkness	Find a boat to travel through the jungle.
Henderson town	Reach Henderson.
Hunter-Seeker	Find and kill all named champion monsters located in dead zones.
Hurler	Kill 100 zombies with thrown melee weapons.
It's an order	Mark 100 opponents which then were killed by your coop partners.
Jetboat	Kill 100 zombies using boat speed boost.
Juggernaut	Kill 100 enemies using charge attacks.
King among kings	Kill special enemies: Grenadier, Thug, Wrestler, Infected, Suicider, Screamer, Butcher, Floater.
Meeting Serpo	Make pact with Serpo.
Military Base	Gain access to a long range radio station.
Mystery solved	Find all the secret files of Consortium.
NewsJunkie?	Find all voice recordings of a journalist.
Professional Tourist	Find all pages from the guide book.
Serving Science	Finish quests for Dr Kessler.
Siege Hammer	Install 5 barricades in any hub.
The Cinema	Clear out the cinema.
The Collector	Find 50% of collectibles.
The Docks	Enter the docks in Quarantine Zone.
The Hoarder	Find all collectibles.
The Hurt Mine Locker	Kill 10 zombies with one mine.
The Storm	Escape from the ship.
Twins	Kill the Twins.
You've tricked me once	Finish the game.