Almost all dealers prefer that you have the money for the pot as soon as you buy it, but a few trusting souls will front the pot to you, and allow you to pay for it after you sell it. Very often, however, they will add a small tax for the privilege.

There are advantages and disadvantages to having weed fronted to you.

If a dealer is willing to front to you, it almost always means pe's not working with the cops (at least not on that particular deal). Cops would rarely give you weed unless they're taking your money and arresting you at the same time. (However, I imagine this changes when people get into the big-time and the police start using more fancy trickery.)

Another advantage, of course is that you don't need to have the money right then, if you can't afford to start dealing on your own.

The problem with fronts come when you start taking too long to pay the dealer back, or when you stop thinking about your weed as being real money, and you start smoking it all and wind up in debt. If you screw up on the first front, only the stupidest of dealers will front to you again, and many will raise their prices on you. So it's very important to pay a dealer back in a timely fashion. Many people get into trouble when they expect it to sell faster than it does.

There's also the risk of retribution if you stiff the dealer entirely. With quantities under five or six hundred dollars, dealers don't usually enact much vengeance, but above those markers is anybody's guess. Stiffing a dealer, obviously, is not something you should ever do for ethical reasons. But also, if you stiff a dealer, you've lost that connection, and if your other friends find out what you've done, they're far less likely to trust you, and therefore less likely to buy from you or sell to you, and far more likely to narc you off to the police if they ever get in trouble themselves.

The point of being fronted drugs, in my opinion, is to save up the money so that you can start working with your own money, which is much simpler.