talkmagic.co.uk

If you have already paid for the secret, is it wrong to pay for someone to build the device for you?

No, it's not wrong... so long as it is for personal use and not for re-sell.

If the preceding is not wrong, then why would it be wrong for someone to build such devices and sell them only to those who have already paid the original inventor for the secret?

When you have PERMISSION to have something for personal use and you have it made, that is an entirely different critter than someone that merely manufactures for the sake of making a buck, which is how I understood your proposition originally (my bad). If it is a limited run, sold exclusively to those persons that have the legal right to said device, then no foul exists; this was recently done with Joshua Quinn's ASCENSION book-test set-up.