Not sure what you mean by 3rd party (as in Paypal, etc... ?), but Authorize.net will allow you to take payments directly on your site provided you meet the requirements to do so (SSL, Valid Certificate, Dedicated IP). I personally have not used it as I prefer Paypal (easier setup in my opinion).

ThePiston wrote:

well I think you can use other merchant service companies and then link those to authorize.net. Or you can use a reseller that does all of that for you, but there's a higher rate for doing that.

Sorry, have not tried this nor have any advise for doing as such. I recommend using one of the payment gateways without linking to another.

ThePiston wrote:

I guess my question is this: is authorize.net a separate service from a credit card processing company - or is it all rolled into one? My understanding is that if you already have a merchant service provider, you can still use that company and link them to authorize.net.

Authorize.net is a full bundled service. It's a payment gateway; in the same manner Paypal works with the major difference of allowing you to accept payments directly on your site and not being sent to a merchant page.