I think it's pretty straight forward, the only pain is the shipping to an FFL. Payments usually go through paypal I think so everything is legit there. I forget but I think handguns have to go from an ffl to an ffl or some FFl's won't accept shipments from non-ffl's....something like that. I'm pretty sure they have to go thru fedex or UPS too, post office won't take em. I'm sure gunbroker probably has instructions somewhere on their site. They do probably thousands of transactions a day so I would say that the system is sound. Good luck
If you have never sold on gunbroker then you don't have a "reputation" built up from buyer feedback. So someone is going to have to mail you money and hope you send them a gun. (unless you want to ship them a gun and hope they send $) I don't have a paypal account so has not been an option for me. I do believe gun broker has some default protections, but.......
The other difficulty is unless you have an FFL you will need to take the gun to your local gun store (LGS) and they will have to ship it to the buyer's LGS (or any FFL holder), but the buyer will need to have their receiving FFL holder email\fax their info to your FFL holder before the gun can be shipped. This is pretty standard but each state does have it's own regulations (many sellers will not ship to CA or a few other states). Also is the firearm legal in the state where the buyer resides? These steps also add costs as generally FFL holders do not provide this service for free.
I have never sold on gunbroker because the requirements listed above were too much of a hassle for me, but one of my purchases has been through non-FFL holding seller so we had to go with this procedure. If you go this route I suggest totake good pics, list everything included, and be clear about a return policy.
You may want to try listing on pennswoods or armslist, looking for a PA resident to sell to. You can then meet at a LGS that is willing to do FFL transfers (usually for a 20$-50$ fee). Way easier and the buyer gets to see the gun before finally handing over the cash. Good luck.
I agree, classifieds and face to face is best and easier. PAFOA has a lot of classified posts. Hate to say it, but used Glocks are plentiful..probably not the easiest sell if you're looking to get the best price. Just my opinion but I think selling items individually may work better for you.