You can always share the fact that you found someone's advice helpful. Online, you can say something like this:

"If you're ever in need of [blank] advice, talk to [so and so]. They just helped me out with a question I had."

Where? If you have a blog, maybe add a random P.S. If there's a place to leave a review, consider that. Or if you're on social media, maybe share a thumb's up with people. They may not need any advice today, but maybe in a month or a year somebody will. Or maybe a stranger, searching online, will stumble across your thumb's up.