1955-1964 Proof Sets Envelopes Sealed From Mint ?

I have purchased proof sets, 1964 and earlier, from my local coin store. They are sealed when I buy them. I do not think the coin store seals them, but purchases them in that condition. So maybe they were opened at one time. I did find a Kennedy enhanced hair in one set. One set had environmental damage to two of the coins. The rest have been normal proofs. Nice but nothing "wow". I guess my point is, know your seller. If you think they are just moving items along, and they took a chance on the condition, maybe you can follow their lead. A random seller on ebay, it may be harder to take that chance.