Anecdotally, I'd bet a Dole Whip that if you search for problems on this site, first for Fidelity, and then for, say,
DVC Resale Market (picked because of size/volume of sales), you'll find the issues with Fidelity to outnumber those of
DVC Resale market by orders of magnitude.
It's not a matter of whether one person had a good experience, it's a matter of how many out of 100 have a bad experience. One would assume that the "majority" of sales for most of the brokers proceed without a hitch. It's the percentage of negative experiences, even if they are in the minority, that make the difference.