I haven't had any experiance but my thoughts are that if you can save the snake from a long journey on the way to you and just buy from a local shop then I would go the shop route.
Plus I think the courier fee from 888 is like £25 or something so it doesn't always work out cheaper.
Also I think if you want a snake that is a reasonable distance away then I would look at driving up to collect it first to see how that would work out.
I agree, avoid using a courier if you can, but people do buy online and I've not heard of many problems. I just wouldn't do it personally unless you have to.