Can u use a Best Buy gift card to buy other mfg gift cards

No, only if its part of BestBuy So say you have a B.B gift card you will be able to purchase a Verizon gift card or cell phone or just apply it towards total bill at the end

I would think not. Stores are pretty particular about their guidelines for gift cards!

I would call Best Buy 1st. I highly doubt it... what would they gain from the sale?

Yes