I have a website with all the information about one city. One of the pages contains a complete overview of all the businesses in this area. For example: you can choose some categories like "Electrician" and then you see a list with all electricians. But this list is full AJAX with JS so I don't reload the whole page.
Should I make some URLs like www.example.com/businesses/electricians for SEO purposes only? When they search for electricians in this area the URL pop-ups in Google?
What you are referring to is a "landing page". They are great for SEO and I would strongly recommend them for your website. It would be best if you could code it in such a way that any new electricians (for example) are automatically included, it would save you a lot of editing time adding and deleting companies on all of your pages. You should consider them for every business variety (plumbing, accounting, etc.) if at all possible.
example.com/businesses/electricians/, or more like example.com/scripts?biz=electricians?
Those are called doorway pages and are one of the most basic violations of search engine rules. A doorway is a page loaded with juicy text content where the user isn't really expected to spend any time engaging the content, the content is strictly for search engine juice and the user is expected to bounce very quickly onto some other content.
Of course if you are using technical means to steer the user away from the indexed content, such as hidden text, screen overlays, redirects, or pushing it way down the page... All the worse.
Generally speaking, if you are doing significant things to your websites just for search engines, you're on the wrong road.
