My suggestion is to add a checkbox to the Store Filters where you can select
stores that are VAT enabled.
Reason being that if you buy as a business you can reclaim the VAT, which obviously
doesn't fly for purchases from private sellers.
So essentially this would allow businesses to find other businesses more easily,
save on their cost price, and increase their liquidity. Finally, this results
in more investment, more Bricklink transactions and potentially lower sale prices
to their customers, because they don't have to compensate the 21% difference
(in case of Dutch VAT) in purchase cost.
I could go into more detail with example calculations of course, if required.