Look at all of the pics carefully for wear and complete packaging. I've seen many items listed as new and the pics showed clearly that they were used.
If not comfortable, ask for more pics. I bought an O42 radius switch track wherein the seller said new and only posted a pic of the box. When I opened it it was clearly well used. The seller disputed that it was used but did refund my $.
As to "test run" for engines, at least you have some assurance that it works. But then it should be listed as "Like New", not "New".
