[quote name='Dad3353' timestamp='1454689014' post='2972130']
A private sale is exactly that; a [i]private [/i]sale. There is no obligation on the part of the seller to reveal who the buyer was, [u]and it's not considered good form to enquire[/u], generally. A buyer usually relies on the good faith of the seller to respect that privacy, including the terms of the sale. It's not written in stone; just a question of etiquette, as suggested in the title of this topic.
[/quote]
IYHO
A 'private sale' can mean as you describe but it also applies to a non-commercial sale. I personally don't think it's bad form/etiquette to make an enquiry; the seller is within his rights to say 'No' but equally I might say "I'll contact the buyer and let him know". It's not unheard of for buyers to fall out of favour with basses as soon as they get them, especially if you can't try before you buy.
I see no breach of etiquette implied or otherwise.