I think there is always a potential for mischief on Ebay, even among many sellers with high feedback. One thing I have learned is that high feedback does not necessarily correlate to a seller's ability to ID trimmed cards. You still need to be sure a seller is reputable and knowledgeable when buying any card of value.
Now, is there less chance of postwar being trimmed than pre-war? I would say if compared to pre WW 1 then yes as so many tobacco and caramel cards were trimmed by the first wave of collectors between the wars. I am at the point I will only buy SGC or PSA graded T cards on Ebay but still buy raw Topps and Bowman there and will do so until proven wrong.
As for market, rarer is better and lots of postwar stuff in nice shape or that is even considered scarce still is relatively high pop. And once you hit the late 60's, there is a lot of product out there.
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