There are many different factors to take into consideration when comparing estimates. First, make sure the estimates have the same scope of work and types of materials. For example, does one estimate feature tile while the other features Cultured Marble?
The amount of service provided by the contractor has an effect on the cost of your new bathroom or kitchen also.
If you want the contractor to handle all details of the project the price will probably be higher. If you want to “be your own contractor” and schedule, plan, and supervise the project, the cost will be less. But make sure you actually have the time and knowledge to manage your project.
Also consider if the contractor has a large showroom, which can translate to a large overhead. This will also increase your price. Finally, if the contractor has all proper forms of insurance the price will be slightly higher than a “pick-up contractor,” who may be unlicensed, uninsured, and uses undocumented workers. Taking a chance with a pick-up contractor is usually not worth the risk.