I think NO.
Sometimes, their buying / bid price is higher than the market, and resale is usually less. Buying a custom auctioned vehicle as used / 2nd hand car is the last priority of any potential buyer, which goes in the market to buy a used car.
And that's why less resale.
Nope. I think, registration is not an issue. They get registered, provided engine / Chassis No. is original and have not been tempered. Similarly, body has also not been changed.
Usually, the cars which go in auction are mostly clear from any legal issues, and if some problems arise before / during registration process, then Customs Department should take responsibility for their mitigation.
I think YES!
Although verification is mostly done against registration No. (here in case of Federal Capital), however, it can also be checked against engine / Chassis Nos. But again, concerned authorities can guide best!
I hope, it helps. Thank you.