Hiring A Company To Do SEO For Your Service Business
The first thing you have to ask yourself when hiring an SEO service is how much money you have and where you are with your business. If you have little money and are just starting out, I would only recommend going for SEO if your area is extremely low in competition OR if you're willing to work on SEO for months (maybe years) without any results.
If it's neither, you should focus on generating revenue first and start SEO when you have money to invest in a 2nd marketing channel. When that time comes, be very careful when hiring someone because 99% of the companies willing to do SEO for a few hundred dollars are complete scams. When you're competing against a saturated market, it takes thousands of dollars to see results (unless you're doing things yourself). In my opinion, if you can't find a good referral, you'd be better off hiring an employee to link build and learn technical SEO for your company.
If you decide to hire someone, ensure you're getting monthly updates to see what they did for the month. You're being scammed if you're paying someone $2,000, and they fixed a few things on your page and got you one guest post on a different site. Don't fall for it.