If someone is selling a pair or trio I would like to assume they are not directly related - parent: offspring, or siblings or half siblings. But I would always ask for as much as the seller knows.
When I have sold hens in the past (and once I get my new stock started) none were/will be directly related, nor would they be, aunts, grand-grand related, etc. - Although as has been said, I perhaps wouldn't know if they were second cousins or something in the first place.
The plan I've been working is that when I go to visit friends and family for weddings or something, I'll look up a breeder online, then buy some hatching eggs from them, and bring them back in my hand luggage. This way I can collect strains from all over the country, without paying expensive postage fees, and its nice to see the set up and parent stock. Long jorneys and plane cabin pressure seem to reduce hatching rates a bit - I've been experiencing around 60% hatch rates, compared to 90% for home bred.