For your first few customers as long as you don't give your product for free for a chunk of time i.e. anything above 3 months all concessions are fair game.

I remember, when we were starting out for the first few customers we went above and beyond to make it easy for them to use the product, if that meant being on call we were there, doing manual data entry we were there, getting them there prospect list we were there.

And giving all of that concessions is very profitable for you over the short term as they become great reference customers for you, which is what you'll need to scale, raise money and get more customers.

I know my next comment will be contrary to popular wisdom, but everyone will tell you do not let the customer drive your product plan or development cycle. Do not build custom features. You have to heed to such advice carefully. It depends on what your solution is and if you are focussed on a specific industry, If it's already on your product plan and you just intended to do it later and need to accelerate it in order to keep the customer happy do it. If it's something that is not on your product plan but the customer is asking for it, figure out if this is something that other customers are/will ask for if not don't build it. e.g. A big customers wants us to integrate to this proprietary CRM. You say NO UNLESS you are going to loose them to a competitor who is willing to do it.

Do not ever make a concession that you will be unable to deliver on. You will loose their trust, which is the most important thing you need to work on with new customers especially when you are new. Be honest and tell them that you will be unable to deliver on what they are asking for in the given timelines. They'll appreciate that a lot more than you failing to deliver.