Now this is a smart scam. He can do exactly what it says on the tin by keeping a pool of extra bitcoins to supplement his users when value falls, but when value rises he gets to recharge his pool with the surplus. This is built on the assumption of a "conservation of value over time" which in the long run is true (if it proves false then bitcoin has failed anyway) but in the short run you could easily have a crash where the net loss by users is less than the backup pool. You are also leaving yourself open to the controller of the backup pool stopping the service or just skimming off the top of it with users having no means of recourse.
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Now this is a smart scam. He can do exactly what it says on the tin by keeping a pool of extra bitcoins to supplement his users when value falls, but when value rises he gets to recharge his pool with the surplus. This is built on the assumption of a "conservation of value over time" which in the long run is true (if it proves false then bitcoin has failed anyway) but in the short run you could easily have a crash where the net loss by users is less than the backup pool. You are also leaving yourself open to the controller of the backup pool stopping the service or just skimming off the top of it with users having no means of recourse.