All of that stuff I buy now from BH or Adorama.
* verified the un-advertised compatibility between an accessory and the device I was buying it for (hours of googling had not been able to confirm this for me)
* explained their personal experience with both the Sony and Canon cameras I was considering
* nearly price-matched another vendor’s sale on a large purchase of Dell monitors
They have their own warehouses with real physical stock ordered directly from suppliers, (no drop shipping and no third party sellers.) One order I received even came with a hand written note signed by the salesman who’d help me select it. A nice touch, but impossible for an operation at Amazon scale.
These days B&H is my preferred vendor for PCs+components, AV gear, SMB network equipment.