When looking at examples of user interfaces, pay attention to how the developer has organized the information and how easy it is to navigate. Does the interface look clean and well-designed? Is it easy to find the information you're looking for?
When evaluating server-side logic, pay attention to how the code is organized and how efficient it is. Is the code well-written and easy to understand? Does it run quickly and smoothly?
When checking references, be sure to ask about the developer's strengths and weaknesses. It's also important to find out if they are able to work well under pressure and meet deadlines. By getting a well-rounded picture of the developer, you'll be able to make a more informed decision about whether or not they are the right fit for your project.
It is also important to remember that you are not the only one who is negotiating. The developer may also have their own needs and wants. For example, they may be looking for a certain salary, benefits, or vacation time. If you are not willing to meet their needs, they may walk away from the negotiation.