how is the best way to eliminate a bunch of BIG stuff and not get shafted cause you're not a salesman? WITHOUT going through classifieds selling piece by piece? All at the same time...anybody done this?
Somewhat moot seeing you have changed your mind, but you have already identified how best to do it except a little nuance could be helpful.
If you really NEED the money, then the options get short in a hurry and KEH and others become your solutions, but for a fraction of the value for the reasons so well covered by others (overhead, profit, holding costs versus how quickly it will move, etc.). Also having stock that does not move can negatively reflect and impact the pricing of the rest of the inventory...
If you have a full system and are prepared to part it out yourself, you can do much better, but time and patience are basic requirements.
You are better to use a phased approach in parting it out, by selling some of the less common but desirable pieces (e.g. ULF wide angle lenses, extremely long lenses, etc.). You could then sell off some accessories (extra film holders, film, etc.), and finally sell a basic kit consisting of camera with one lens and a couple of holders.
Otherwise you will be paying directly (commission or profit margin) or indirectly (reduced price to you) for someone to do that for you.
While there may be a number of people interested in some of the more interesting stuff (WA and long lenses), few will want to take everything unless they think they want it themselves or can quickly and easily part it out themselves, hence reduced price to you...
And yes, I have been one of those who in the past (less so now) who have bought a total system to get a few items I wanted and parted out the rest. The result was often getting the bits that I wanted for little or even free after it was all done, so I know the scenario well...
Good luck with whatever you decide,
Len
