The buyer is willing to spend $70 (asking plus shipping) for the item. He has paid you.
You will be spending $50 shipping cost plus whatever the monitor cost you in the first place plus your eBay and Paypal fees. Will that be more or less than $70?
Newbies, both buyers and sellers, tend to get excited.
Perhaps there are cheaper monitors available, but it seems an elaborate hoax to obtain a $20 monitor.
The buyer is in NY most quotes were exactly $50.
Pack very carefully. Doubleboxing would be good.
You might even find it worthwhile to have such a fragile item packed 'professionally' by UPS or FedEx. Those companies also include tracking and insurance in the cost of shipping.
And there is no worry about doorstep fees, Americans can import up to $200 before duty kicks in. *
If you cancel the transaction, the buyer can leave feedback. And Detailed Seller Ratings.
*There is a long running thread about UPS doorstep fees to Canada. But we pay duty in imports over $20CDN (~$15USD)