Most people put a flat-rate postage designed to cover postage and handling. Other will say things like "buyer pays actual shipping costs," which I do when I have extra boxes laying around and use my UPS account to ship. Some will say "actual shipping + x".
The few others which say "shipping determined after auction" should be mitigated by eBay's shipping calculator, or not bought from, period.
I use eBay's shipping methods and calculator, which is usually dead-on, in my auctions. If I offer Priority Mail or UPS, then I use eBay's options for these. It only takes a few extra seconds to set up and doesn't cost extra. Aside from that, eBay has a space where you can include extra handling charges.