Have you checked their feedback? If they have decent fb, have a long history with Ebay, it should be ok.
I would warn you however that you are not covered under paypal protection policy unless you are shipping to a confirmed address. Only the US and certain Canadian and UK addresses are eligible. Singapore is not.
To ship to Singapore, only accept Postal money orders to avoid any false claims of non-receipt by Paypal. Send the item with tracking via USPS global express so that you can give a status update of your item in case the item is held up in customs. Let the buyer know that the cost of the item does not include any customs fees incurred.
If for now you are only trying to sell within the US and are just making an exception in this case, try changing your personal settings in Ebay to block bidders with a non-US ship to address. If you do want to make an exception, there is an exemption block list on Ebay you can add the International bidder's name to.
Also, in Paypal under "payment receiving preferences" you can block non-US payments as well. This is to ensure they don't "accidentally" pay you with paypal.
Sorry for the novel! Good luck with your transaction!