Don't worry about playing hardball in the negotiation. You can preface your negotiation by saying something like this.
"As long as we're on opposite sides of the negotiating table, I am going to do my best to get a fair share of possible upside from your company, and a decent salary. When we conclude this negotiation fairly, we'll be on the same side of the table and working towards the same goals."
"Now, I want half a percent and $110K."
Keep in mind that your BATNA (best alternative to a negotiated agreement) is to say, "No thanks. Good luck." They need to hire somebody: time is money at their stage of business. You don't need to jump into their job.
But don't have this conversation at all unless you think their business idea is worth five years of your life.
Yes, this is one of your best sources of leverage, as long as you can take your time and be picky (which you absolutely should be able to do if you're a working programmer).
The longer you keep them talking to you, the better. They can't waste time forever, and their own sunk cost bias works in your favor.
"As long as we're on opposite sides of the negotiating table, I am going to do my best to get a fair share of possible upside from your company, and a decent salary. When we conclude this negotiation fairly, we'll be on the same side of the table and working towards the same goals."
"Now, I want half a percent and $110K."
Keep in mind that your BATNA (best alternative to a negotiated agreement) is to say, "No thanks. Good luck." They need to hire somebody: time is money at their stage of business. You don't need to jump into their job.
But don't have this conversation at all unless you think their business idea is worth five years of your life.