In this day and age, authors keep hearing the question "What is your promotion plan?"
It's a reasonable question for a publisher to ask. They want to know that you're actually going to help some instead of just ducking back into your writing cave. (That lifestyle, sadly, is not available unless you're really famous and probably not even then).
Here's the thing, though. Unless you have an agent and are going to a big New York publisher - then authors need to ask smaller publishers the same question.
I recommend that before signing a contract, you ask the publisher what their typical per-book promotion is. And if they don't have a plan, what are they offering you that you can't do yourself?
If the answer is "We partner with authors on promotion" and that's all they will say, then you probably want to keep looking - because, sadly, that often means "We don't actually do anything. It's all on you." At which point you might as well pay the up front editing costs and then keep all the royalties - because they're not helping.
Look for answers such as "We have a good relationship with these reviewers." Or "We can try and get you a Kirkus Review" (very expensive for self publishers).
Ask who pays for promotional materials. If it's you, then what are they doing for their fifty percent? If the answer is that you pay for the ones you distribute and they also distribute materials they pay for - that's a lot more reasonable.
Do they have a good relationship with librarians and independent bookstores?
What can they do that you can't? That's probably a question all authors should be asking when they sign with a publisher.