There’s a slight difference in meaning between shop=vacant and disused:shop=*, and both can be used in combination:
shop=vacantmeans the storefront is currently vacant.disused:shop=*means whatever used to be in the storefront is no longer there, but whether the storefront is currently vacant is less clear.
Around me, many storefronts are built years before the first shop occupies them. The shop is no longer under construction; it remains vacant but has not fallen into disuse. shop=vacant is the only tag that can be used in this situation.
When a shop moves from one neighborhood to another, I immediately retag the former location as disused:shop=*, but I don’t feel confident tagging it as shop=vacant until I’ve surveyed the site to make sure some other shop hasn’t moved in already.
Often a disused:shop=* lingers even after a new shop arrives and is tagged in shop=*. Technically, was:shop=* would be more precise for this situation.