As both an investor and a licensed contractor, I'd share some insights on how to screen contractors:
1. If you are not knowledgeable nor experience in an area, set multiple appointments with as many contractors as possible to make yourself feel comfortable, especially in a more complicated project. You will find that the more people you talked to, you will become more and more knowledgeable about the project. Interviewing contractors is your job, so don't blame that there are no contractors available. The good ones will always there, it's your job to find them. Standard practice is minimum 3 quality bids, and often you are gonna reach out to maybe 12 people to get those 3 bids. So don't be like a lazy investor called two numbers and no one picks up then you said no one likes to work in this area.
2. I think most people know this by now: Cheap is usually not the best. But I would also add expensive often does not mean better. The truth is, you can't negotiate with a contractor if you don't know their cost. Some people are happy with little profit and can still produce great quality work fast, but other people like to charge you an arm and leg and sub out the work to cheaper labor anyway. So when you analyze the price, you need to understand the cost and their profit. Almost all labor cost savings are generated from a more efficient process rather than going for the cheapest rate. If I pay someone $100 an hour that took them 2 hours to complete because they work efficiently that's far better than I'm paying some one $30 an hour that took them 8 hours to complete.
In order to know the cost, you need to have all contractors to bid with the same scope of work. If you are new, I would walk with the contractor on site, tell them what they see is the "initial condition", then show them a photo and tell them that's the end result. This way they can't later come to you and say "well the access was tough and I need to charge more" or "I gotta do so much prep work so I have to charge more" So they need to provide a quote to take the initial condition to the end result. Include clean up and trash haul off. As far as the rough goes, usually it's hard to find those specifications so you just need to talk to each person and get a feel for their rough process.
3. When you received multiple bids, if there are bids that are so much cheaper than the others, call that bidder and ask if the bidder included this this and that (typically you get these from a bidder who spelled out the details in their bid). If the bidder said those are extras, have them resubmit or if they said those are included, you should have them wrote it in the bid based on your comfort level with them.
4. Job qualifications. The easiest way to go about this is to ask them to show you similar work that's being done recently, cheery on top if they can provide customer references (not a deal breaker if they don't because not everyone is comfortable with that). But you gotta be mindful about the situation. Most likely the super good ones are working for a great customers and they are probably very busy and may not give you a real bid or bid on your project at all because they think it's a high chance you are wasting their time. So the chances are, the ones who are gonna bid on your project with a decent schedule would be the ones that aren't so busy right now, unless the market is just slow for everyone. So you may or may not be able to get to see people's recent project that's similar to yours. But for those who can produce them quickly, sending you 3 sites to go visit, then I would immediately feel good about these people.
5. Payment terms. Something else you gotta factor into the bids. Anyone who charges an initial deposit before the job starts will be low on the totem pole. Anyway you can take the job and not needing to get paid until the job is done gets to the top of the list. Especially for people whom you've never worked with before and they are asking a large sum down for "material." Most of the time, I could work with the contractor to give me a take off and I order them and delivered to the site so I know my money is going into my material not funding their Ponzi scheme (contractors are the world renowned ponzi scheme masters).
Just keep in mind, people are in business to make money. They aren't in this because they love doing it (maybe 1%). And investor is notorious for wanting to making most money themselves and leave nothing for the people who work for them. If that's how you operate, you will quickly find no one likes to work for you. Sure you can take advantage of one contractor on one job, but if you are serious about real estate investing, you need to have a crew who wants to work for you. That means they are making good money from you. (Don't simply see how much money you are paying them, understand how much profit they are generating from you.) The cost is cost, you aren't gonna negotiate below the cost, so the key to get the price down is to understand people's profit margin, and then how well you are at negotiating how much they are gonna take home at the end of the day.
Lastly, pay people fast. As soon as the job is finished, pay the people for what they've done. If you are working on a bank draw and can't pay like in 30 days, let them know ahead of time so they can be prepared.