They take into consideration the size, weight and declared value of the item. All items do get charged some kind of duty, its only very rarely that I've been able to avoid duty for my R/C parts. But usually they won't try to extort you, unless you lie about the value and get caught in the process. I bought my netbook on ebay and got it sent through EMS, and I only paid something like LKR1800 to get it cleared. It depends on a lot on how humble you are (I kid you not), just smile and answer their questions but don't say too much. Also I wouldn't advice on getting down a camera or any other fragile item like that, because the packing is going to be huge, and it's going to cost you a mint to bring it down here. Limit electronics to small, cheap items. For anything else, get a mate to send it to you from abroad.
P.S. Declaring a lower value and/or marking the item as a gift will be irrelevant if you're asked to come down to the parcels section; they *will* open the package and slap a duty on it, especially if they figure out there's been deliberate undervaluing.