As seller I used to compare different options, there are tons of shipping one can buy online, a part standard postal shipping, dozens of different parameters, weights, sizes, countries, registered, unregistered, etc.. At the end I could offer different options: the cheapest, the cheapest and fastest, the cheapest and most secure shipping, something like that. It was easy and friendly. And buyers were happy they could choose the shipping they prefer.
I spent a couple of afternoons trying to fill the form of discogs, no way, it was impossible to fit the best shipping options. So I guess every sellers chosed one standard shipping that usually rised the cost.