Amazon is a perfect example of this. Their site is convenient, Prime is handy (even though their streaming is useless), but it's their customer service which made me 'loyal.' Over the years, I've had a few items arrive damaged, including a few very expensive ones. The customer service calls seem to take at most 5 minutes. For instance, I had a computer arrive completely destroyed. I called them, explained what happened, and the rep asked whether I wanted a refund or replacement. I said "replacement," and she replied "I'll have it to you by tomorrow."

That level of service, as a consumer, means so much to me.