How do I pay?

Don't do it! 
I had a deal for a lot less money ($650) and the dude ripped me off.

Sometimes the seller will have a validated profile on eBay or audiogon so ask him that. Otherwise escrow.com 

The answer to the OP's question is: through the nose.

I had an instance when a seller refused to use PayPal due to it's fees.  I offered to add the Paypal fee to the asking price and we did the deal that way.  I refused to do the deal w/o protection and was willing to pay a premium for that protection.

How close to you does this seller live? If no shipping is involved I think Misstl has it right above. Plan to pick the speakers yourself and bring cash to his house after you make sure he doesn't live in a dicey part of town. If you like them after inspection/listening, help him load them onto your vehicle, then pay him and drive home. I’d like to see his receipt for them too from when he purchased them originally, just to be sure they are not stolen merchandise. Having had worked 25-30 years in Corrections, I can assure you there are an awful lot of crooks and con-men out there.

Mike