For a used Essence, it would have to have a few upgrades to go for $2900. That is entirely possible. It's also possible that a store would try to retail it at $2900 even if it would be unlikely to fetch quite that much in a private sale. Note also that prices on used Alembics have dropped a bit with the economy, so a store that doesn't follow them might easily be mistaken about value. A Blue Book doesn't have much chance of getting it right with all the factory customizations that occur on Alembic instruments and generally low volume of sales.
As far as the Rogue selling for way under $2900, how quickly did that sell? Two to three weeks, right? That bass was a great deal, and some would call it under-priced.
It will take an understanding of the configuration of the Essence and probably some pictures to get a fair estimate of value from the crew around here. Even then, there will be a range of prices the bass could sell for. The higher in the range you ask, the longer it will take to find a buyer.
As far as the best venue for selling, a sale here usually occurs at a fair price and to someone who will appreciate the instrument. Members who have been here for a few years are also less likely, IMO, to be scammers than the typical internet population. As a new member yourself, buyers may look for some extra assurances from you.
You would possibly get a few dollars more on eBay, but there are all the hassles and risks of eBay associated with that, including paying for a listing that might not result in a sale.
-bob
