For the purposes of this subpart, the claimant, or owner, shall be treated as having borne the ultimate burden of an amount of tax only if:

(a) The claimant or owner has not, directly or indirectly, been relieved of such burden or shifted such burden to any other person,

(b) No understanding or agreement exists for any such relief or shifting, and

(c) If the claimant or owner has neither sold nor contracted to sell the articles involved in such claim, such claimant or owner agrees that there will be no such relief or shifting.