I also wouldn't ask or even hint at feedback.

I have several sold items where the buyers haven't even let me know if their item arrived, but I figure if after two weeks or so I haven't heard from them, then there must not be a problem.

I leave feedback once they pay, because they have kept up their end of the deal, so to speak, and I archive after a week.

If I get feedback after that, great, if not, oh well.

In saying that, I am waiting on a few from my jewellery, since I only recently began selling it, and I desperately want the feedback left to show potential buyers my jewellery is genuine and not cheap junk.

Patience is a virtue.