Has anyone sold over $35k worth of equipment over the net? How do you protect yourself?

I would never pay with wire transfer. I have sold some pretty expensive speakers. The guy came to my house and paid in cash. It's the best way for both parties. He gets to hear the product and the deal is DONE that day. It does shrink your potential buyer pool. I have sold electronics through the mail. No problems.

Very few platforms like ebay do anything to protect the seller. In most instances the buyer is king. 

To be clear, escrow services like escrow.com exist precisely for this purpose - to protect both buyer and seller in an expensive transaction, and they charge relatively modest fees. Buyer sends money to the escrow service, the service tells seller to send the equipment to buyer, and there’s an agreed-upon inspection period. If the buyer is satisfied, the service releases funds to seller. Otherwise, buyer sends equipment back to seller (at their own expense), and once seller confirms receipt, escrow service returns funds to buyer. There’s professional dispute resolution if things really go south, and it’s certainly still very useful to vet the counterparty before the transaction - but this is mostly a solved problem.