Advanced PayPal API integration

I need a developer that understands PayPal APIs very well. We have an online consumer to consumer market that uses a lot of the PayPal APIs from PayPal verification to delayed chained payments... The majority of the API integration is already in place but we need an expert to come in and make sure everything is set up right, do bug checking or provide us with possible better solutions. New API integration is needed as well We use adaptive payments (delayed chained payments API) needs checking and improvement Preapproval API (needs checking) Refunds and partial refunds needs to be set up (not done) Use PayPal verified API Will need to incorporate some of the simple direct payments APIs Fully custom shopping cart (mostly built) needs some improvements