i will weigh in with some general guidelines.
A glock 22 is worth $500 at best, i don't care how few rounds you fired, its used and in low demand and high supply.
An ar rifle or lower marked "law enforcement only" is not worth a penny more than one that is not marked. No one cares, stop trying to market stupid roll marks as value added features.
Seeing as a stock colt ar can be had for a bit over $1000 new, your no tier low end used and bastardized/customized rifle isn't worth more than the new price of a colt. It sucks, but that's the way the cookie crumbles.
Selling an ar upper without bcg and charge handle is plain dumb.
A "rare" firearm is worth less to those who actually shoot as opposed to collect firearms. In addition, if its rare because it sucked and is of poor quality then its worth nothing. If its rare because it has low numbers or is out of production and is a quality and sought after make/model, its worth more than normal, but not mid to high four figures.
A customized firearm has been modified, not necessarily "upgraded". If your modification includes anything from ncstar/leapers/utg it is the opposite of an upgrade.
Regardless of whether or not you shot the firearm, it is still used. You bought it, you want to recover as much of your investment as possible. That value is not retail less the tax, nor is it $10 less than retail and tax, and its definitely not more than retail. I don't care what you paid for it. Market value is dictated on availability and lowest available price. Paying more for your item because you are either incapable or too lazy to shop around is not my concern. At the very least you should search the first 5 pages of current ee ads to determine what the going price for your particular item should be if you expect to sell it.
You cannot collect tax legally without a registered gst/hst number, so stop asking for full retail and the tax. You paid it, you eat it.
Pictures sell products, no pics no sale. The vast majority of sold! Ads were accompanied by pictures.
Accessories can add value, if they're accessories that are in demand or desired. Cheap sh*t holsters, lights, sights, slings or other useless junk do not add value. Furthermore, failing to separate said items from the overall "package" will reduce your chances for a sale.
Finally.... A used ruger 10/22 is worth no more than $300 shipped. New 10/22's can be had for $279 all day long.
Tdc
eta: Dewats are paperweights and aren't worth f**k all.