Great idea Bruce.
98% of my collection has been bought through eBay.
I also go over the photos as closely as possible and will ask the seller questions like "How did you come by the engine"? and will ask for additional photos if warranted.
If I am successful in my bid I always send the seller detailed packing requirements, like removing and packing the chimney stack, whistles, burners etc anything that can come loose and rattle around and scratch the hell out of everything else. I ask for good packaging and prefer double boxing and offer to pay a bit more for the extra expense.