There are basically two ways people handle this.
One way, and the way I endorse, is to always check before the first date. It takes only 3 minutes to call, and the answer is very specific- yes/no.
The other way is to wait until it is getting “serious”. People who endorse this say that there is no reason to check if it is not serious anyway.
I do not understand this.
Firstly, there is no reason to not check.
Secondly, you create a new ritual in the relationship called “checking dor yeshorim”. I think that is foolish, since relying on meaningless symobolism in the place of meaningful interaction is bad. If you feel close to her- tell her. Don’t hint it through absurd rituals.
If I date someone and I like her, I say, “I like you”. If you can’t communicate your feelings with words and meaningful actions, you don’t have a very honest relationship.
Thirdly, there is really no reason for anyone to ever have to go through the feelings of liking someone and being cut off because of dor yeshorim incompatibility.