I've noticed a lot markers and equipment being severely overpriced lately (as what usually happens right after x-mas) so I thought I would offer you all some friendly advice...
1: Study your marker and resale value.
-uses your resources. Ebay, the forum, the nation, whatever it takes to find the average resale value of similar markers. If everyone is selling them for 200, theres no way you're getting 400 out of it.
2: Upgrades do not raise the value of your marker
-ya know, they may a little, but that depends on the upgrades and the marker. As a rule of thumb you may as well assume the upgrades are "freebies" to attract attention to your marker. The general population will look at a marker with ups first, but wont necessarily pay more for it. (it takes away the whole "customization" aspect of it)
3: The "showroom floor" syndrome
-much like a car, you may as well cut the value of your marker in half as soon as you (or your aunt mable) buys it. Just because its NIB or LNIB doesnt mean anyone will pay retail for it. Like the upgrades, saying "LNIB Mini!!!" will attract attention, but dont assume you will get $450 out of it. Oh, and if you say "LNIB" it had better be LNIB or better, because if they're expecting a flawless marker the smallest scratch will cost you in the feedback department.
4: Trade value
-now this ones a biggie. Rule of thumb: he who has the more unique marker wins. An example; marker A and marker B both have a retail value of $500. If there were 5000 of A and 50 of B made, then you're going to have to sweeten the deal to get marker B.
5: "But Jester, what can I do to keep the value of my marker?"
-Well, Jimmy, there are a few things you can do to keep the resale on your marker from falling faster than a strapless dress on prom night! First, extreme maintenance! keep it clean and well maintained! Dont do any PERMANENT alterations! Remember the upgrades thing? If you keep all your original parts, throw them in before you sell them, then sell the upgrades seperately and you can *sometimes* make more money! Also, no one wants a spraypainted superman symbol on the side of their marker...except for you...and shaq...And lastly, and probably most importantly, KNOW THE VALUE OF YOUR MARKER!!! Nothing makes me happier than when people over estimate the value of their equipment! Believe it or not, its actually EASIER to get people to come down off the price if they think its worth more than it is. All that proves to me is they didnt do their homework. I've bought many a guitar for less than half of what I was intending to sell it for that way.
6: Dont be afraid to ask questions.
-If you dont know what your markers worth, the forum has an appraisal section. Or ask me, or one of the mods. We can help you or at least point you in the right direction. Just dont be disappointed if we tell you somthing you dont want to hear (no, your Ion is not worth $800, sorry).
7: Your memories are NOT for sale.
-Therefor they do not add to the value of your equipment. "But, Jester, I've had this marker for 2 whole years! It means a lot to me!" Well, then dont sell it. Just because said marker got you the winning kill that scored you 3rd place in your local fields tourny does not make it worth any more than retail.
8: Listing proper condition.
-Heres another tricky one. This will cost you in more ways than one. If you have spray painted...well...anything really, then you CANNOT list it in "great" "perfect" or even "good" condition. I see a lot of this in masks, but what you have to remember is this: Masks flex, bend, and take a LOT of abuse. Spraypaint does not. The key to this is
BE HONEST! If your mask is scratched up, its scratched up. Lenses can be replaced. If your hopper has a crack, it has a crack. Shells can be replaced. If your girlfriend gripes too much, she gripes too much. Girlfriends can be replaced. (see a pattern here?)
Again, these are just some friendly tips. Follow them and it will save you, me, the mods, and baby jesus time and trouble.
Mods, if this is in the wrong place feel free to move it, delete it, ban me, stalk me, whatever you gotta do

Just wanted to put my years...and years...and years...of retail experience to good use.