Seller Silence

There is absolutely no obligation for a seller to answer your questions,  though it certainly would be courteous and beneficial to both parties. 

I see courtesy as a kind of obligation, one that especially benefits the seller. That said, the buy has the option to walk away or, if the purchase happens eventually, leave a rating of the seller that downgrades them for the communication component of the transaction.

I have had warranties where they specifically stated whether they were transferable. Seems like a reasonable question to me since the seller is in possession of the warranty and knows if they bought it used or new.

For example,

All Pass Laboratories products purchased new from an authorized Pass Laboratories dealer in North America are covered by a transferable, limited 3-year warranty. This warranty includes all parts and labor charges incurred at the factory or factory specified repair facility, exclusive of any subsequent or consequential damages. Damage due to physical abuse is specifically excluded under this warranty.