Our web programmer needs our merchant account information to set up our ecommerce site. He is asking for the "processor name", "processor ID" and "merchant ID". If I provide him with the information is he going to be able to access our merchant account and take money out? ie. charging refunds to his credit card.
Could you be more specific as to your situation? How is the web programmer in question related to your company? Is he a permanent staff or a contractor? A proper contract should protect you reasonably well from such threats.
In more technical terms, there is no reason why your programmer needs your actual credentials. Sites like PayPal provides sandbox environments to test out transactions without actually involving actual money. Your programmer should be able to code the transaction system and provide a configuration interface where you can add in the actual details yourself later on.