That's a long time to wait,and it sounds like you've been patient so far,but the waiting can drive a person a little nutzoid.
And yes,it may be due to an accident,illness,whatever.
But in my book,an honest seller would either be comatose, dead,or would have had someone contact you by now,to explain.The 'no responses' part,IMO, means it's time to stir up a response.
Here's how:

Call your credit card company now,today,on their 800 #.
Ask for their Fraud Protection Dept., or whatever they call it there.
Tell them you believe you may have lost $750 online, in a possible scam?
Don't make direct accusations;just describe the situation.
In several States,if not all,theft of >$500 online is a felony.
Although the seller is presumed innocent until proven guilty, the credit card company is required to report it for investigation by local authorities.
And if he has a business license,also to the Better Business Bureau.
Because if he fails to pay you,then it is up to the Credit Card company to reimburse you;if indeed you were scammed.

>>>No credit card company report; no possible fraudulent claim for them to pursue ( or end up paying! )<<<

Next, contact PayPal and tell them you've filed a report with your credit card company.

[ To contact PayPal Customer Service by phone,go to PayPal online,log in,click on "Contact Us",you will be given a 6-digit 'Customer Service PIN #' which is good for 60 minutes.Then call PayPal @ 888-221-1161 and tell them you have filed a possible fraud claim with your Credit Card Co. ]

Even if you reached a humanoid by phone @ eBay, at this point,it's not their problem...Eventually,they can ban him if he's a fraud,but your settlement will come from either the seller,PayPal or your Credit Card Co.

eBay is just the 'store window' you bought it from.

I'm a Psych & Chemical Dependency R.N.; not a lawyer,but this worked for me last year.

Apparently,the Police in his hometown must have gone to his door and asked him about his intentions to settle this,or face charges.
Because he sent me a refund...a bank cashiers check,overnighted by USPS.

Sorry this is so lengthy,and Good Luck,

~Gnarly