Just received my first batch of e-bay purchased eggs today.
The seller is very professional! The eggs were wrapped in tissue, than well wrapped in bubble wrap, then placed in a box with crumpled newspaper. The box had a slight crunch, but not a single egg was cracked. I candled the eggs and can't see anything amiss, but I've yet to see air sacs in such young eggs. The breed is one which I have hatchery type, the seller claims his are show. The eggs I received today average larger than the eggs my hatchery hens lay, so I'm pleased.
This seller has excellent feedback, which contains information about his packing skills and there is feedback about hatch rates and healthy chicks. I suspect if the seller used better pictures, his eggs would sell faster, but since, if I have a good hatch rate I'll want to order more, I won't tell him that yet.
I've also purchased here, and had a fine experience. Well packed eggs, an acceptable hatch rate.
As others say, learn what you can about a seller before buying and you will most likely be fine. Assuming of course, the postal service doesn't jinx you.