Usually you give your friends a friendly discount because it saves the hassle from advertising, packing, etc. and also your friends return the favor.

But I would never sell something expensive to a friend, period. There be dragons.

I'd be inclined to pay more for it getting it from my friend than on a second hand marketplace. It removes the chance I'm going to be scammed, or the product isn't as described, or the seller will leave me a bad review.

On the other hand, I wouldn't ask my friend to pay more if selling, so maybe a par price is fair.

You hit all the salient points.