At this point I feel I have a 6th sense for purchasing the right flips. It's just you know it when you see if sort of a situation. But here's what I can beat describe what is the basics that go through my head:
1. Location. I know. Cliche. But the better the location, the higher you can go price wise when it's all finished.
2. Once I've figured out my ideal location, I obsess over the market there. I watch everything that is buying and selling, I go look at everything, I see what solds are and I know the area like the back of my hand. So when I see a deal, I can recognize it immediately and pounce. Honestly, most of my deals are pocket listings, so it helps to know the local realtors, etc as well. But I take my time and am very very choosy. Don't get too hasty in excitement to get started because that can come back to bite you later on.
3. Lot. Lots cannot be changed. If it's on a busy street, or it's unusually small, or is at the bottom of a sleep hill and gets flooded when it rains, that's a dealbreaker for me. Again, your sales price will be hurt by these things and sellers will get turned off by them, and you can't eliminate the busy street or eyesore power lines or water tower across the st, etc.
4. The house itself. This is the trickier part and can be specific to where you are looking. For example, I'm working in an area where people will pay much more money for a single story without steps than a two story, even if the two story house is much larger. There are a lot of older people around and they don't want steps. So that was something I looked for, though wouldn't matter as much (or at all) in other areas, or for me, personally.
If the foundation is messed up, or there's something going on that, yes, I can fix, but it will be on the truth in housing report and will scare people off, that can be a dealbreaker.
If walls need to be moved and the place is crazy, that's a head scratcher. Getting one with a reasonable layout is ideal, but you might get a better deal in the wonky place and with some creativity get rid of dated/strange distractions without it costing too much.
If you can see an opportunity to add a legal bedroom, that always a bonus that isn't too much work typically and adds a good amount of value. When I was in the Midwest, a lot of times it just meant adding an egress window!
Buying the nicest house on the street - the comps will drag the value of yours down. I avoid buying the biggest home in the immediate area.
Small master bedrooms or master bedrooms without ensuite baths - buyers don't like that. Try to create one or buy a house that already has that. Also, master bedrooms that are right next to other bedrooms, I've noticed, people don't like that either, especially if this is going to be marketed to families with children. They want their space away from the other bedrooms.
Lack of closet space turns buyers off.
Can't think of anything else right now, but hope that helps.
-M