And yes, lots of business owners do work on a "goodwill" basis when it costs them next to nothing, in the hope of future custom.
Once we went to Blackpool illuminations and got stuck in a traffic log-jam, literally didn't move for over an hour. DS getting more and more desperate for the loo, so we went grovelling into a restaurant we were stuck outside and politely asked to use the loo. We expected eye rolling/sighing and to be told we had to buy something (we would have done), make a charity donation, etc., but the waitress just smiled, said "of course" (she could see the standing traffic) and showed us the way. Because of that, and that alone, we went back a few days later to have a meal, so it definitely worked for them (and we told them why we went back so they knew that a little goodwill does work sometimes!).
Same with my business. Years ago, a couple came in asking for some very simple help with their tax returns - literally a 10 minute job for me to simply explain something to them. They offered to pay, but I was having none of it as it was a quick and simple job. A few years later, they bought a business and appointed me as their accountants which was a job worth £2-£3k per year to me. I'll never know whether they'd have still appointed me if I'd charged them £25 for the "advice" years before, but in my mind, doing that kind of freebie work is marketing.
Another example, a fuse blew in my car and I went to the local dealership (who I'd never used) to ask them how to change it, as I couldn't get the fuse box cover open. Instead of telling me "the trick", the service receptionist came out and opened it for me, then went back to get a fuse, put in it, closed it up etc - all in all, about 5 minutes. I asked him how much we owed and he just waved us off saying it was a freebie as it didn't need to go into the workshop. We then took the car to that dealership for it's services and bought our next car from there too.
Goodwill in business is a big thing. Lots of times it doesn't get repaid, but sometimes it does, and the good often outweighs the bad.