I ordered NEO 1:43 '59 Oldsmobile 98 Hardstop shown below for my layout about two weeks ago, through that big river website. You will find this same model on several other model train/diecast model sites, too. It is a cast resin , not metal, and like all NEO models both very intricately detailed, and not cheap.
Anyway, this otherwise lovely '59 Olds is very slightly warped, I think due to being fastened too tight to its pallet. Note in the photo below it droops just a bit at both ends. Anyone who was around these much knows they did not "droop" at the ends like this. Removing it from the pallet and inspecting it underneath confirmed is is bent slightly: the chassis bottom is slightly bowed down at the ends, too: the whole car is very slightly hogbacked.
I've indicated in the photo below what I think caused that. This model, which is resin, and about as thin as i have ever seen resien cast, was fastened down quite tightly by two screws. The one at the back had about 7/16 inch leverage to the rear wheels, the one in front only 1/4 inch, but I think too much tension on on them put too much tension on the resin which "flowed" slowly over a period of weeks/months? - anyway I think this caused the tiny bit of hogback the car has as it sat on the shelf at the wholesalers/was shipped to me.
Regardless, I am not going to return it as the warping is not perceptible unless you are at eye level with it. Here it is on the layout and it looks splendid - just as I wanted. I have never run into type of warping before, and am glad it is not severe - this time. I don't know if other NEO models will be warped, but I thought I'd pass it on - one more quality problem to worry about when ordering stuff for the layout!