SEO. What to look out for. What to ask

SEO ? What to look for ? What to avoid ?

Hey folks. I’ve used PPC for a long time with mixed results. I know the long term value of SEO , but find it difficult to figure out who is who and what to look out for. A lot have excellent reviews, and I see pricing vary by a ton. I’m in a highly competitive space (business lending) that works across the US. What types of questions should one be asking a prospective SEO company to make sure it’s a good thing ? Cheers.