This...
I generally like to post here first. If no interest, then go to gunbroker.com. As long as items are fairly priced and you are patient, 80-90% of items sell here. Good pictures are critical.
I've sold some here and a few on gunbroker. If they don't sell here you can always try gunbroker, before your first feedback you will have a NR rating and a warning '" that if you see this item on another website it may be a scam", so it makes the first few hard to sell. Rimfires I may try here or at rimfirecentral's classifieds. On gunbroker, I generally list it for the minimum I want out of the gun, you can always change the listing price if you do not get any bids... But I never use the "Reserve" feature, because I never bid on them or even look at them, anymore as they are a waste of time (usually).
Yes, no fees here (or other forums), gunbroker has as noted above fees, an auction house is generally much higher than gunbroker. And I never sell (except for consignment) at any of the local gunshops as they will offer you a pittance, at least in my area. Gunbrokers listing fees are only a few bucks, and you can easily set it up to automatically re-list until sold (you are not charged for the re-list when you use this), you are only charged the fees noted above if the guns sells.
Good pictures will help a lot. Crappy pictures will make the gun harder to sell or it will sell for less than it is worth. Conversely, try to picture all of the blems or describe them.
$100 a rifle for shipping is way high. Actual shipping (I'm on the west coast) will run up to $55 maybe $60 max. insured (weight and distance dependent of course). Boxes can be had for free at local gunshops, start getting them now, don't wait for your first gun to sell to start looking for boxes. Pack it well, insurance claims are a bother and may not be honored if it was not packed worth a damn. I like to use bubble wrap and extra cardboard at the muzzle and butt. Handguns can only be shipped through the postal service by an FFL, NOT an individual. Handguns can be shipped by an individual at the private carriers, for to much, it costs me the same to have a dealer ship a handgun priority mail as it does for me to take it to a private carrier (UPS or Fedex), it all depends on what your FFL dealer charges.
Know your product... some firearms that may not seem all that nice or a famous name brand may be highly desired by collectors or shooters. Trying to think of examples... Remington Nylon 66's, 'some' Savage 99's, oddball rimfires, etc.
Jerry