@j1477 - here are a few resources that may help you in your search for a solution:
1. You mentioned reserving an amount on a credit card. You can do this one of two ways. First, you can authorize a credit/debit card and then settle it at a later date. Authorizations do go stale after a few days (the general rule is 7 days, but it varies bank to bank) so if the time between authorization and settlement is greater than ~7 days, you'll need to reauthorize to complete the transaction. Also, authorizations cannot be settled more than once. For example, you can't authorize a card for $100 and then settle it twice, each for $50.
The second option is to do an Account Verification request. Here is more information on that: http://bit.ly/NlKuG
2. The second thing you mentioned was "transfer part of the buyer's deposit to a seller". I may not understand this correctly, but this sounds like you're collecting payment on behalf of a third party, which is known as aggregation and is one of the highest forms of risk in payment processing. Here is more information on that: http://bit.ly/775RkJ
If you're looking to transfer funds to payout out another provider, you could also move the funds via electronic funds transfer (EFT) from your bank to theirs.