A warm welcome
That's sort of a no-brainer, but when you travel solo I found it really important. You have many kilometers in your legs, you might have not talked to anybody the whole day and a little smile and kind words do wonders. Most of the campsites did a good job, but I had as well two which I would never ever visit again, as the staff was almost hostile. And there were some that excelled, here three examples of great hospitality:
The day that I stayed at Confolens was a tough one. For quite some weeks I didn't have any trouble with dogs, but within ten minutes I had very close encounters with a fierce terrier, a mixed dog, and a German shepherd. When I came into Confolens, I was passing the local campground. Nobody was at the desk, so I gave them a call and they immediately came and booked me in. They were super friendly, had icecream and even drove the chair that I borrowed to my pitch. Throughout the stay, I decided to actually stay for two days, the owners were super helpful and always up for a chat.