"First paying customer" but then you're blaming products

With respect, can you really question the ability of certain products at this stage in your career?
Experience is the key, and you can't be knocked for not having it because we all have to start somewhere

I think the most important thing is always trying to improve yourself and follow best practice, which results in experience. When you're experienced you know exactly what result to expect from every single carpet you clean. So don't beat yourself up, it might have just been one of those that wouldn't have got much better.