Hi Joss,
The question is which one knife would you buy for the purpose of a 10 year investment.
You have to remember that in actuality there are very few custom knife buyers on Bladeforums or Ebay.
The number who routinely purchase $2,500 on either location would be few if any. So basing your conclusions on these sites are probably not the best places to gather good "intel".
You bring up a vaild point. If your going to buy a custom knife for the idea of investment. You should probably do your homework and find out who the buyers are for that type of knife.
As with any investment if you use a broker (paintings, coins, stocks, bonds, etc.) you will pay a commission. After all the reason you are going to these individuals to sell your investment. Is the years they have spent in that field earning their reputation and connections. This will help you divest yourself of your investment in a timely manner.
Don't forget if you choose to sell the knife yourself. You will have to at a minimum spend your time and probably some money to sell the knife. So there are costs associated with selling directly from seller to buyer. Make sure you dedcut that (those) costs from the commission.
Also, don't forget any profit you make is considered a Capital Gain. The IRS would like you to send them their portion of your profit....and they didn't do anything to help you sell the knife. They are worse than dealers!
All that aside Joss. What $400 knife would you buy for a 10 year investment?