Welcome to Gaia! ::

imho, when it comes to store bought items, sell them at a discount, i'm ok with 75% off, if you try to get full price for something a gaian can get in a store, you may be in for a loong wait.

gaming items,
flowers, trash, bugs, ect: kinda worthless, sell for 1g if you're lucky...

tickets, do not sell for less than 2g per. you can go as high as 2.5g per,

go to the gaming item forum:
http://www.gaiaonline.com/forum/viewforum.php?f=125

to find some people buying for good rates,

or you can vend in the marketplace to try your luck. in my experience, selling tickets for 2.0-2.3 per ticket will get an instant sale, you can sell them as high 2.4-2.5 when there aren't alot of venders selling tickets at that moment,

fish
i dunno, i just sell the commons for 3/4 full price, uncommons full price, rares double/triple full price, legendary.. i dunno, never caught a legendary.

monthly online collectables:
don't sell these until 3 months after you get them at the very very least. this is the ONLY thing that goes up in value over time...

lemme know if i missed anything, or if i was of any help to you at all.

what i do is i go on to the market and find an item thats price is bouncin up and down (sealed leters at the beginning of a month) then i set it fer about 2 or 3 k higher..or if it is a sealed letter (which i buy ushually for 13k) sells fer about 20 k just before the opening time of that item.....

just remember that you should collect at least 1 or 2 of the monthly items and save them...they sometimes end up in high demand...unless it was that damn momo or ufo sweatdrop