I don't have a lot of deal-breakers but they're more difficult to overlook especially now that I'm older.
Smoker. Many women are smokers and it's automatic no.
Single mom. Also hard now that I'm in my 50's. Only caveat I would make is if you had adult kids and we were just casually involved. You have a 20 year old that lives in another state? Maybe. You have an 8 year old and the dad is around all the time? Nope.
Loud, bossy man haters. You know the type. No thanks. I'm a grown adult that is capable of conducting my own life. I don't need another mother I don't listen to. Also any feminist SJW's. Way too emotional and unstable.
That really narrows it down doesn't it...
When I met my wife, she had a friend who smoked so she smoked (very lightly) socially. I asked her to stop smoking, which she did, and never picked it up again (and now finds smoking as offensive almost as much as I do.) So yes, there are social smokers who are capable of kicking the habit, but nonetheless, I waited 2 years to marry-her-up so there you go.
And that's perhaps the most important thing: women are big into "red flags" and "deal breakers" and little sh*t tests for the first month. These tests often are either beaten by bad boys or sidestepped altogether. There is no substitute for a reasonably long engagement period particularly in high-risk feminized cultures. The first few dates or even month of courtship can be irrelevant to long term performance. I'm reminded of The Bachelor franchise: Relationships are set to classic Disney style courtship and fantasies (there's literally a "fantasy suite" at the end for pre-marital sex) but when Real Life finally begins, at least 3/4ths of the relationships fizzle out. And this is under ideal circumstances: no financial concerns during courtship, big engagement rings, lavish dream dates, etc.
So the best way to deal with red flags is to see how the person performs during the pre-engagement phase AND handles conflict. For the frst month or so, when women hold all the cards, all bets are off. Even in non-game countries, there's a high demand for young women so they can get away with being spoiled and unreasonable with men they barely know. Essentially, dating a woman, particularly in western countries, is like being a clown at Chuck E Cheese trying to entertain a room full of kids with food they can throw at you.
After emotional connections are made, how does she handle rejection (in the sense of not getting her demands met?) Does she walk off and not come back (there's always a first time, for their little sh*t test, but after that bluff is called, it's moot and mine knew it.) Do they become vindictive? Get drunk and nasty? THAT was a red flag with one girl I dated and I dumped her right away. It was ok for her to be irked at me for not buying her something but she got drunk, smoked, and threatened me so that was that.
Between initial courtship/gaming and actual marriage, there's the period where one can and should set boundaries. How will this person treat you 20 years down the road when you're in sickness and for poorer? If you say you're not going to take them out to an expensive place, do they accept that judgement? (It's ok if they get p*ssed about it. But do they walk?)
I think the primary problem for many western men, particularly the blue pilled, is that they didn't want to look for red flags at all because they were too busy trying to "seal the deal" and pleasing the woman. Most tigers are cute and cuddly if you keep them well fed. Pre-Martial courtship therefore is sort of like flirtation which requires men to slowly build emotional rapport with the woman and then set expectations higher and higher to see what she's capable of. Almost like raising a daughter. General rule of thumb: Before the wedding, the woman should already be PERFORMING up to standards as if she was married to you for 10 years. She should be thinking in terms of budgeting and care about how much going out cost just as much as you do.
Regarding if she has kids. When I was young, it was a deal breaker. In hindsight, I realize I left a lot of good women on the table. Yeah, most of them were attention-whoring bimbos sleeping with bad boys but in my generation at least, some were just nice young women who wanted to start a family and married the first guy who was polite and nice to her. Provided the father of the kid is not a problem AND she knows and takes responsibility for what went wrong, there's potential there. (Hindsight) I'd rather a respectful father relationship with the kid than an absentee loser who gives the kid daddy issues.
As I said in other comment elsewhere, biological clock tickers are another kettle of fish and in some ways, more dangerous than (decent) single mothers. Particularly in the west, there's a toxic stew of caveats: Is she 30 and has baby rabies and nervous issues? Has she been frigid that whole time and focused on her career? Did she sleep with a lot of chads and is now looking to "settle" but may never be satisfied?
Ideally, a young man should marry at the age of 23 or so to a young woman that age or younger, that he's known for a few years at least, but in these times of austerity, that may not be possible for most.