While many of my happy clients give me a testimonial, they also sometimes surprise me with a mention in the acknowledgments or in a signed book.
After a book has been published, I will usually purchase a paperback copy—and sometimes authors will generously send me a signed copy—and they all go on my editor’s bookshelf. This is a gallery of the nice things they’ve said about my editing or beta work and our relationship. It always brings a smile to my face!
For the record, I really wish the US would lean spelling preference toward acknowledgement.