Owner of The Dog Nanny- a 30+ employee cage-free boarding, daycare, and grooming facility in Massachusetts.
Any specific service category has its own unique areas that you can add value to your customers/potential customers. But what every industry is advice, just like you're seeking. Without needing to be an industry expert on a subject.. most sales reps will have a broader knowledge base on many topics than your customers. Being able to get simple questions answered and get a baseline of info on certain areas is hugely valuable to everyone.
In my industry (animal care), being able to offer customers a 90 second-5 minute conversation with some advice on a minor problem takes minimal time out of my day.. but can add a ton of valuable in their life.