I have written a lot of reviews. Some places, like ebay, give you a jump start. You can click the number of stars, that sort of thing. Some sites have little check boxes - was the item as described? Did it arrive on time?
Writing a review, in prose, is like writing a blog. I often tell people if they can write a letter, or a postcard, they can write. In fact, that's the best way. So imagine that you are just telling someone about your experience.
Tune Keys tuned my piano recently. The piano hadn't been tuned for a couple of years, and I know that it was starting to sound a little flat. It took about two hours, and Russ not only tuned the piano, but he cleaned off the dust and "crud" inside of it. I had no idea that the importance of that! The piano sounds great!
And that's it. No need for stilted, formal language. No need for "advertising hype". When people read a review, they want to hear your opinion. And if something caught your attention, mention it. And if you really had a problem and want to complain, start with the business. If they don't respond, and don't take care of the problem, write them a bad review, starting with "I contacted Acme Exterminating...."