Is there such thing as honest SEO companies?

I am starting a local plumbing company that specializes in toilet installation and toilet repair. I've been looking for an SEO company and it has been a nightmare... complete nightmare. How do I know that they are doing what they say that are doing? Most SEO companies want to give you an 'Analysis' every month. How do I know it's not some BS white paper from a SEO plug in? Should a legit company give me an itemized breakdown? Some companies want 20% of the Ad spend to manage Google Ads and others want flat fees of $500-$600. Everyone 'wants to help' and they always say that the other guy is doing things wrong. It gets confusing. Help