Offer letters can be accepted as proof of income most easily when a tenant has arrived new in town and hasn't yet started work. Applying for an apartment?Yep, as long as it states start date and salary you're good. I'm a leasing agent and do this all the time. Mention your name, the type of job you do, and why you're interested in the apartment. You could get an "employment letter" from your company which states that you are an employee along with your joining date and salary. Fill Out the Application Completely and Accurately. Fill out the application completely and honestly as possible especially the required fields. Generally a job offer letter will show your new salary and that will help that you will be financially able to pay rent. Learn how to write a proof of income letter with our stepbystep guide and use our fillintheblanks template as an example.