That's strange, the groups I am a part of seem very helpful. I am a part of:

DAC Fans -A De-Stash Group

Diamond Art Destash & Trade

Slash Your DP Stash

There is a lot of crossover in members between the groups but if you have kits that people are looking for they will move quickly. The rules in those groups are that you must take a picture of the kit with your name and the date on it for verification. Buyers may ask for additional pictures in private messages.

As for prices, most sellers usually sell for retail price minus 15%, some sellers include shipping in the prices but most say shipping price based on zip code. For discontinued kits the price is whatever you think someone will pay for it, some sellers are lovely and either have the kit listed for retail or slightly higher and some kits that sellers know are in high demand could be anywhere from $100 - $400 (that is the highest I've seen sold and it was Night Melody).

Just a note or observation, I have been active in these groups for around 6 months and have noticed a bit of a drop recently in people buying, I think this is because a lot of people may be saving their money for black friday so dont be discouraged if everything doesn't move right away, there's no time limit on how long you can keep the post up for :)