I used to get really worried that my customers thought their nails were no good when they didn't return, but as has already been said some peeps only book for hols, occasions, xmas etc. They may not be able to afford regular maintenance and you will most likely find that come next spring/summer they rebook for their holiday nails again.
I have stressed big time over this over the last few years particularly when I started working in a salon for the first time, I thought that my boss would think the customers weren't happy with my work. But it is completely normal.
Also, you will find that you get customers that you will wish didn't come back :lol:. Personality comes into it too. Some clients you just don't get on with or click with and they may not rebook even if you do a stunning set on them just because there was a wrong vibe between you if you know what I mean. At the end of the day (being a Young Nails tech myself) you are using a fantastic product that your clients should be happy with.
Don't take it personally, just take the payment and be happy they came to you in the first place, each client is a learning experience. If you know you did something that they may not have liked then learn from it and use that knowledge with your next client and of course practice, practice, practice!!!!!