packaging: double-box, abundant use of bubble-wrap etc.Wrap each item separately (i.e. mains plug, ICs, speaker cable, component). Add as many stickers as you want - "Fragile", "Electronic components - useless if dropped", "This way up" etc
I'd recommend using interparcel.com. Numberous bad experiences with ParcelForce (inc a recently damaged amp!). Insure for the full amount. Take photos of the items pre-packaging and once packed. Email the photos to the recipient - if they look any different on arrival have the recipient take photos pre-opening, and then of the item unpacked.
Rob
Edit: the points above related to packaging/sending. As a seller you want to make sure you receive cleared funds which cannot be clawed back by the buyer, e.g. cash, bank cheque, Paypal gift, bank transfer. As a buyer you want buying protection, e.g. Paypal payment for goods. Many agree on Paypal payment for goods/services (mandatory for you to offer if selling on eBay). If selling away from eBay and the buyer wishes to pay by Paypal, you may want them to cover the 2% cover Paypal will make on the amount received.