Retail I would say very low, maybe even fractions of a percent. Wholesale I would imagine we probably get a majority of sales. There's no way to be sure how much there is of something that isn't reported though.
That said, for retail comps you don't really need completeness, as it isn't a very liquid market and retail sales have little predictive value. As long as you can find a few good comps for any domain you're negotiating on I think you're good. We do have tens of thousands of retail sales, maybe even a six-figure number.
Wholesale is where I think completeness becomes more important.