Also, what's the TOS on this referral promotion? IIRC, for many services these referral codes are for private distribution and forbid this sort of thing.
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For example, the Uber policy:
>Uber may, in its sole discretion, create referral and/or promotional codes ("Promo Codes") that may be redeemed for discounts on future Services and/or a Third Party Provider's services, or other features or benefits related to the Services and/or a Third Party Provider's services, subject to any additional terms that Uber establishes. You agree that Promo Codes: (i) must be used for the intended audience and purpose, and in a lawful manner; (ii) may not be duplicated, sold or transferred in any manner, or made available to the general public (whether posted to a public form or otherwise), unless expressly permitted by Uber;
Reading it again that might not actually say what I thought it did.