Mastering Technical Sales: The Sales Engineer's Handbook

By now you should have a feel for the time, expense, effort, and implicit risk of doing a trial. Because of the high cost, you should only engage in a trial when you know you can win, and when a win will result in a sale. If you aren't sure of either of those points, you should seriously consider trying to avoid the trial.
Ask your customer if they have done product evaluations before. If they have not, be prepared to help them establish a clear decision process. You will also have to be very sure they have access to appropriate technical staff to make the trial happen, unless you are providing all of the hardware. You might also ask if their salespeople perform trials with their own products. You may find them more sympathetic to your requests if you can establish common ground around trial requirements.
Your sales representative may be uncomfortable with this, but you should get your customer to pay for any trial that takes more than a day or two of your time. The only exceptions to this are if evaluations are especially common in your industry, or if the customer is a major partner or a strategic account.
You can offer to have the costs of the trial applied toward a future order. This is another good qualifying technique. If your customer wants a trial, but balks at the expense, then...