please help me to revise this paragraph

I’m fed up with the mistakes that our current accounting firm makes. I run a small construction company, and I don’t have time to double-check every bookkeeping entry and call the accountants a dozen times when they won’t return my messages. Please explain how your firm would do a better job than my current accountants. You have a good reputation among homebuilders, but before I consider hiring you to take over my accounting, I need to know that you care about quality work and good customer service.

Again ... do you need this to be more concise and less negative? More formal? Or what?

less negative and formal. thanks

This is the first part to revise:

I’m fed up with the mistakes that our current accounting firm makes. I run a small construction company, and I don’t have time to double-check every bookkeeping entry and call the accountants a dozen times when they won’t return my messages.

I'd start by omitting the first sentence or revising it and putting it later in the paragraph. Make the first half of the current second sentence into the first sentence of the paragraph. The rest of this paragraph should be two (or maybe three) sentences with the other ideas in them, but without the obvious anger.

Try revising just that part first before diving into the rest.

Writeacher's advice is excellent. More generally, I'd eliminate all the complaints about the current accounting contractor and just state that you are considering a change in the accounting firm you employ. Then ask how the alternative firm would provide a service with emphasis on accuracy and customer service. It's good to state that the firm you are addressing has been recommended by other homebuilders. Positive reinforcement often gets good results. Being critical of another firm is not a good idea. It makes the letter-writer sound like a complainer, and the new firm may not wish to engage with a chronic complainer.

Weekness and strenght

Oh, boy, do I feel your pain! Dealing with accounting mistakes and unreliable accountants can be a total circus act. But fear not, because I'm here to help you revise that paragraph in style and with a touch of humor. Here goes:

Enough is enough! I'm running a small construction company, not a clown show, and I can’t keep juggling bookkeeping entries and chasing after circus performers, I mean accountants, who never return my calls. Now, before I roll out the red carpet and hire your firm, I need to be convinced that you guys aren't just another bunch of jokers. Your reputation among homebuilders is impressive, but can you show me your magic tricks when it comes to quality work and top-notch customer service? Give me some assurance that you're not just here to sell me a ticket to the circus!

To revise this paragraph, you can make a few changes to improve clarity and coherence. Here's the revised version:

"I am becoming increasingly frustrated with the mistakes made by our current accounting firm. As the owner of a small construction company, my time is precious, and I cannot afford to double-check every bookkeeping entry or spend countless hours trying to reach our current accountants, only to receive no response. Before I make a decision about hiring your firm to handle our accounting, I would like to know how you can provide a superior service compared to our current accountants. While I have heard positive things about your reputation among homebuilders, it is important for me to understand your commitment to delivering quality work and exceptional customer service."

This revision clarifies the main concerns and expectations you have while expressing the need for reassurance in terms of quality work and customer service.