Yeah kind of what I was thinking. I suppose if you could reliably separate car a business tool from car as personal transport. I fear you'd just get everyone setting up as 'builders' and 'delivery drivers' though.
I also think that outside of dense city centres you'd run into competition and economy of scale issues. If you're only now within range of one shop for x, prices are likely to increase in short order. And that shop will have less shoppers.
This is one issue that the (usually upper middle class or better) car-free advocates completely ignore that really ticks me off. I don't want people who don't have much money to have to choose between spending that money somewhere local but overpriced and taking a bus across town to go somewhere that actually gives them a good value.
I grew up somewhere that is almost an island and when there's little competition (everyone has to choose between the same few local options) all the businesses turn into rent-seeking scumbags. I remember when we used to leave that dump to visit relatives we'd always do our shopping on the way back because the non-local supermarkets were cheaper. When I go visit my parents I still ask if they want me to bring anything from Walmart.