Most NAPA stores in my area are marketed toward repair shops and other commercial businesses. They offer delivery, monthly invoicing, and have a broad range of products. At one position I held, our shop ordered almost exclusively through NAPA for the most common items. Their service provided saved us a lot of time and expense. Their pricing reflects those services, IMO.
As someone posted earlier, repair parts through Rock Auto and other online merchants is the best deal if you have the time to wait. These days, for my own fleet or relatives/friends, I'll usually call O'reilly's or Advance Auto for common maintenance parts.
FWIW, I don't buy WD-40 unless I'm cutting bulk aluminum because it's an adequate coolant that's easy to dispense. It's also been many years since I had to squirt a small equipment engine's spark plug wire in the rain, WD-40's other useful property. I use other sprays for penetrants, corrosion resistance, and lubrication that are far superior to WD-40. WD-40 also attacks some rubber and plastics. It's a long story but I nearly lost my life to it's use aboard a tank vessel at sea. IMO, it's basically a ripoff all the time unless you like coconut oil and solvent on everything.