I often strategically buy &/or acquire items for trading that others will like.

Scientist: Botany

Human, Raptor, Flyer, Spitter, & Bruiser items: (Very High)
Tyrant items w/ 1+ copies: (Very High)
Tyrant market items w/ no copies: (Very High)
Tyrant store items w/ no copies: (Very Low - Low)
DO NOT ASK for the last one unless you're offering:
a. Unobtained Tyrant store items
b. 2-for-1 Tyrant store muts
c. 3-for-1 Tyrant store skins
If it seems too high, it's because I really don't want to trade them in the first place, but I won't pass up CONSIDERING a good deal.

a. Renamed items
b. Steam-designated untradable items that are visible in Inventory but not in trade windows
c. Some store items have clones that are neither orange nor marketable
d. Most bandannas, collars, etc. don't have any type OR class
e. Some Human skins are in Human Cosmetic type

Keep abreast of upcoming event items w/ PCE's Special Event Items [trello.com]Trello board!

If other avenues of trade compensation aren't enough, I also recognize ADEQUATELY demanded market items from both PCE as well as other games. Fulfillment acceptance probabilities are denoted in parentheses in the cost intervals below:
5a. <$0.10: (Zero Chance)
5b. $0.10-$0.19: (Very Low)
5c. $0.20-$0.39: {Low)
5d. $0.40-$0.99: (Medium)
6d. $1.00-$1.99: (High)
6e. >$2.00: (Very high)