Sites do not fail suddenly. They drift, and the owner stops looking at their own site the way a stranger would, and then one day somebody mentions that they could not find the phone number.
Here is what I look for when somebody asks me whether theirs is due.
It is hard to use on a phone
Open your site on your own phone right now. If you have to pinch to zoom, if the menu button does nothing, if the phone number is text you cannot tap, it is done.
Three quarters of the people looking at your site are on a phone, and for local businesses it is higher than that. This is not a style question.
The information is wrong
Old hours. A price from two years ago. A staff member who left. A holiday notice from a Christmas that has been and gone.
Wrong information is worse than no website, because somebody drives to your shop and finds it shut. Sometimes the real problem is that updating the site is annoying enough that nobody does it, and that is a fixable problem.
It takes more than three seconds to load
Test it on mobile data rather than your own wifi, standing outside. Sites built five or more years ago tend to carry enormous uncompressed photographs, and every one of those is a person who left before your page appeared.
You are slightly embarrassed to send the link
This one is unscientific and it is the most reliable signal on the list. If somebody asks for your website and you find yourself saying “it is a bit old, but”, that sentence is the whole diagnosis.
Nobody can update it
The person who built it is unreachable, or the system needs a password nobody has, or the login goes to a company that no longer exists. A site you cannot change is a leaflet, and leaflets go out of date.
What redesign should and should not mean
It should mean the same content, faster, on a system you can edit, with your prices and hours in front. It usually takes about six weeks and it is not the dramatic reinvention that agencies enjoy selling.
What it should not mean is starting from a blank page. Whatever your current site is, it contains years of small corrections that somebody made for a reason. I read the old one carefully before I replace it, because half of the useful content is already there, buried under a design from 2017.