One of the reasons I buy from PBR is they charge you the EXACT shipping fee (based on weight and size), and they add a handling fee. When you recieve the package, it is packed really well and the box is the exact dimensions. Marco, on the other hand, find the biggest box they can find and rip you off. My last order had more packing than parts, and some of the parts were missing.
Combined shipping is "hit and miss". With eBay auctions, I always ask about combined shipping on items I want BEFORE the auction ends. Years ago, I bought a Aux Lamp driver from the USA, and I asked if the seller had a Squark and talk board - which he didn't. But a month later, I recieved the aux lamp driver board in a much bigger box - which immediately angered me - but when I opened it - it had BOTH boards ! He was kind enough to GIVE me a board and he charged me the exact shipping fee.
A while ago, I bought a heap of Tamiya stuff from Chine. It was less than half price than Aussie and USA site, so I bought 20 items - But I FORGOT to ask about the EXACT shipping cost - as the seller specified he would combine shipping. The order cost me AUS$24 - and he charged me AUS$20 to ship. Originally, he wanted $26 - which was the individual item shipping price simply added. I refused to pay until I recieved the actual shipping cost. When I recieved the package - I looked at the stamps and added up the Hong Kong Dollars - it cost him AUS$6.55. RIP OFF !!
Lesson learned - I always ask what the EXACT shipping cost will be.