When we got ours fitted we paid our local builder to do all the hard work, so we had no problem with any of that. I think if you are taking on a task such as we did, gutting and starting again getting someone in is the only way to go.
Regarding aftersales, I never had to go back to them with problems, all we had were leftovers, like extra shelves extra, which I was able to take back and get our money refunded! Which I have to admit I was very pleased with.
The delivery of the kitchen was fine and free, we did make sure that we did not book the builder in until we had everything and we had double checked it all.
I think the thing with Ikea is that you do have to do alot of hard work yourself to make sure you have everything, but if you do overbuy as long as it is unopened/used, they will give you your money back, or credit note if you've lost your receipt. That makes an awful lot of difference I feel.
When we bought our kitchen I was damned if we were going to have some disgusting one from MFI, and the £1200 we spent at Ikea was well worth it and I would do it again, except I don't think I would have the solid wood work surface, it takes too much looking after, especially with children around.