In regards to some of your payment terms, the buyer can't add $3.50 for registered, or $1.50 for gift wrapping at check out, they can only pay what is on the invoice. If you want them to have the option of registered, you need add that to the invoice before sending it. Have your standard mail as the first option, then underneath it will give the option of adding another postage option. Put the reg post there so they can decide. Not sure how you can add the $1.50 if they decide they want gift wrapping. Be aware though if that is part of the transaction, you will pay fees on that $1.50.

Also, if the buyer is paying by PayPal they can't leave their user ID as reference, but you will get a message saying who has sent the payment through and what it was for.

You mentioned with the PayMate that you will be running promotions and to check your store for details......you don't appear to have a store......

As already mentioned, remove the mention of leaving negative feedback, because you can't leave it and buyers know that. It's an empty threat and looks silly.