I charge a fee to visit sites and find out why something isn't working. I also charge a fee if something has to be coded or changed to the site to make it work. This has worked for me for decades of design, however a client recently asked me if I charged still for visiting and did not fix anything. My reply:
Is this a serious question? I have never had a client dissect my time vs charge so much.
Usually, if it can't be fixed it has something to do with your host or host settings.
If it will help you to be at ease then I will tell you that I usually (Emphasis on usually) will only charge if I end up adjusting or fixing something but its not always the case because sometimes finding out why something does not work takes time to test and try different things to find the cause.
Therefore, let me ask you… do you think I should be spending time on people's sites for free? If so, next time I go to the doctor to check my health I will have to ask him if he will also charge for the prescription. Next time I visit the dentist I will ask if he will charge me to check my teeth and then charge me if he has to clean or do fillings.
Professional visits, unless otherwise stated costs money because of this equation: time = money.