It’s difficult to ascertain whether this SEO is legit or not. You’re giving us your tainted view of him and we can only see things through your lens.
There is hardly anything objective you have said apart from the software he uses and that backlink software can be used on tier 2 properties.
Everything seems to stem from the fact that you just don’t like the guy and are subjective. No contract, it’s a good thing – most SEOs sign a 12 month retainer with clients. The boss wants him to teach you SEO. He’s doing the bare minimum to tick the boxes, every minute he spends teaching you, is a minute wasted doing actual SEO. So blame your boss not the SEO.
A few things you can do to ascertain if he is legit or not.
Is he building fresh content, once every 2 weeks or weekly and posting on your site? (he should do that).
Is he building useful content, longform 2000+ word pages for important pages like homepage and other landing pages? (he should)
Is he building good clickworthy titles and descriptions for search results pages? (he should)
Is he working on optimising the company site for speed? (he should)
Has he done keyword research and grouped keywords into categories and built pages for each thematically similar keyword group?
Now the links part.
Is he doing outreach/guest posts to high organic traffic sites related to your niche?
What type of links is he getting from this software and where are the links pointing to? Hopefully not money page.
Others may want to add their questions.
The comission basis is a silly way to pay the seo. Just pay them their consulting fee. If the SEO comes from word of mouth recommendation from another business owner who has had good results, I would say that’s a sound recommendation. Better that than signing onto an SEO that spammed you in your contact form.