pretty simple.. Don't charge back on valve unless you are able to prove it wasn't you that did the charge. Period.
...and don't use Paypal since
they may reverse your transaction without your consent...
...or claim a refund if a product or service purchased through Steam
closes prematurely...
...or
import a game which Valve (rightly or wrongly) thinks is illegitimate...
...or falling foul of any part of Steam's
Subscriber Agreement which includes (section 5) the clause "Valve may terminate your Account...for any conduct or activity that Valve believes...otherwise negatively affects the enjoyment of Steam by other Subscribers." so posting a negative comment on Steam's forums could qualify for termination.
