#9 Do they offer discounts easily or without you even asking?
If they send you a price and then offer a discount early in your conversation, that's a red flag. While it may seem awesome at first, just think about it. It'd be the same if you went into your work and told your boss to cut your pay by 30%. You don't want to give up your income, and neither do photographers.
It's a sales tactic to make you feel like you're getting a great deal. It's the same reason every car dealership is constantly offering $10,000 off. Don't be fooled by it.
#10 Presentation as a Business
Let's say you have $5000 budgeted for a photographer. You narrowed it to two, good job by the way, I know it was tough! So, Photographer #1, who has a beautiful website, sends you a gorgeous price list and great information to hopefully answer any questions you have.
Photographer #2 sends you an email with a paragraph or two of text just talking about basic info and they also charge $5000.
Both photographers are the same price, but based solely on how they present themselves should be a huge factor in your decision making.
It's all in the details. You want a photographer who is detailed oriented and who is willing to take the time to show you the best of what they can offer. If Photographer #2 is unwilling or unable, then why do you expect them to take the best photos possible?