A Medigap policy is a newer insurance type to the marketplace that was created by private industry. The idea behind it is that it is intended to cover the gaps that are left behind by Medicare (thus the name). Some of these policies can be rather complex to someone who has never dealt with one before (most of us have not). Therefore, it is usually a good idea to get an agent to help you understand everything in the Medigap policy.
This type of agent works for the insurance company. It is their job to try to help you to understand what all is contained within a Medigap policy. It is also their job to try to convince you that you absolutely need this policy. You should keep that in mind and not get tricked into buying anything that you don’t need. That being said, most agents are honorable people who are not going to try to pull any tricks on you. You should trust this person and listen to the advice that they are giving you on which policy might be right for you. They are the ones who have much experience in this area and who know the most about these plans.
You are welcome to buy your own Medigap policy without the help of an agent. Doing so may be a mistake for you though. If you end up with a policy that you do not need or want, then the fault rests with you. It is a huge financial decision that you are making, and there is no reason why you should not seek the advice of others.