(I do think a slight discount often makes sense just because a friend is probably quicker and easier to deal with. But anything more substantial turns into asking for free stuff, and yes and no are both perfectly fine answers to that.)
Yes dealing with friends is nicer than strangers - but also when you're selling stuff, sometimes it's better to do strangers. Expectations of long term service and support are clearer and have more defined boundaries.
Declining to give you $600 out of the blue because you'd rather have more money is not being indifferent.