Just to get one thing out of the way...everything is negotiable.
Although some brokerages have certain commission rate policies.
But either way, just because an agent offers you a "deal" doesn't mean you are bound to sign an agreement and go with that agent.
Especially if you feel uncomfortable with the situation you are being put in.
I'm with Bigtoe and Agent007 regarding selling first.
Especially if you need the cash from your current home to buy your new home, I would list it.
If you are seriously uncomfortable with that option, and feel discouraged because you aren't finding the right home for you, I would check with your lender and look see if you might qualify for a Bridge Loan that would enable you to buy first and sell after. There are added fees, etc. So talk to your lender about this and other possible options.