Agents get commissions on supplements (and supplement renewals), too. Unlike fixed-rate Advantage commissions, supplement commissions are based on a percentage of the premium, and the commissions on supplements are generally (maybe even always?) lower than on Advantage plans.
FWIW, no agent sells every plan available. They're required to disclose that, but I think it's something people don't really think about. It's one thing to go to a Kia dealer and know that all they sell is Kias, and if you want to look at a Toyota, you have to go to a Toyota place. Everybody knows that. But in the Medicare field, you might not even know Toyotas exist.
SHIP counselors provide information about Medicare on a volunteer basis, if paying a commission bothers someone. But even they don't necessarily know
everything, and they might still have a bias for or against Advantage plans.
www.shiphelp.org/
Picking one's flavor of Medicare is a minefield. If you have the money, having Original Medicare and a Plan G supplement is the obvious choice--the most comprehensive coverage available with the least hassles.
Well, except you have to pick a supplement company. The good news is that all supplements under the same letter (like Plan G) have the same benefits, and they have no discretion in what they pay toward Medicare claims--if Medicare pays, they pay. So theoretically it doesn't matter which company you choose.
However (there's always a "however" with Medicare), some companies are known to engage in a practice called "closing the book," where they freeze enrollment in a supplement, and open a new supplement with tantalyzing initial premiums, only to repeat the process in a few years. The frozen supplement's premiums go up and up because its membership is all getting older, and there are no younger people offsetting the aging people's increasing claims, and people who can pass underwriting to get another supplement abandon ship.
Granular details like that are not necessarily the province of SHIP counselors, and I'm pretty sure they're not allowed to recommend one company over another anyway. So even if they said, "Now, be careful because some companies have low premiums but they incrase dramatically later when they close the book," what would you do with that information?
Even so, a SHIP counselor would be a good starting point, and their mandate is to offer information, and they don't sell anything.
Again, if you have money, Original Medicare + Plan G Supplement is the way to go, and if you choose the wrong company and end up in a closed book and can't switch supplements, your excellent coverage will continue, only at a higher price.
But if you can't afford OM + G, then you have decisions to make, taking into account money, hassles of getting care, limitations on coverage, comparisons of specific Advantage plan benefits, not to mention predictions of the future. Just what every older person wants to do.
Personally, it was easy for me. I'm a traveling fulltimer and Original Medicare + Plan G supplement covers me wherever I go. Plus it's much cheaper than my insurance when I was under 65, and provides better benefits (my only cost above the premiums is my $240 Part B deductible).
I found a Plan G supplement (AARP/UHC) that includes gym memberships (very common among Advantage plans but relatively rare among supplements), so my choice was clear. I'm very happy to be lucky enough that I can afford it.
(I also have a Part D prescription drug plan, for about $10/month. I don't take any maintenance drugs, so the usual advice on picking a plan doesn't apply to me. And predicting which expensive drugs I might be prescribed for a condition I don't know I will develop is beyond my abilities, so I just got a plan with a low premium.)