Well, I'm not sure where you saw this, because I've just come from that web site, and have read the provider Contracts & Policies for Mystery Shopper Services, which is, as you say, a division of BES....here is a copy/paste of their Payment Policy right from their contract:
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Please note that a W9 form and IC Agreement are required. Payment is sent out 45 days from when the shop has been edited. Under special circumstances dictated by the client, reimbursements may be handled differently and sent out earlier than the 45 days. In such cases this will be noted in the shop notes.
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Where did you see this exactly???