Ask HN: How do/would you handle custom feature requests for a SAAS?

So let's say that you have a SAAS and you are just starting out. You are past a certain stage where you have something that already have a few paying customers. You reach out to more potential customers but suddenly, you have a lot of potential customers asking for feature add/updates. but you are a SAAS. You do not want to customize it too much for that specific client. How do you handle this ? If you tell the customer "sorry", then you might lose them. If you entertain their request, you are getting into the dangerous territory of too many custom versions of your app which might not be sustainable as you grow further.