I will gladly pay up (some, of course) for a dive shop with good service, stock, and convenience. I used to live literally across the street from a dive shop. Assuming competence, I would've been happy to pay ~10% more than online for plenty of things from them. it would've built a good relationship with the shop, which would mean that any parts or toys/tools I needed were available that day instead of waiting a few. It would've been a convenient place for fills before long trips. It would've been a great way of meeting divers.
I first visited that shop right after I got my Intro to Cave Cert, and I've spent an upsettingly large amount of money on dive gear since then. That shop could've earned nearly all of it had they been reasonable. They weren't, though. I found another shop that's gotten the vast majority of my business since then. That shop is 7 hours away. I've been to that shop more times this year than I visited the local shop in the 4 years I've lived here.
Just remember that if you go online only, you'll only have online. That means air fills and that-day deliveries aren't going to be an option. Support local if having a local shop matters to you, but figure out what it's worth. After my second interaction with my local shop's owner, I doubt I would've given them any of my business regardless of their pricing. After my first interaction with my currently preferred shop's owner, I figured they deserved a chance to earn my business.