Most people scramble on the first deal. The buyer list that looks established almost always started with a frantic phone tree when someone had a contract they needed to move in a hurry.
Here is how the list typically gets built in practice. Somebody controls a property under contract, meaning they have agreed to buy it at a set price and have the right to assign that contract to someone else for a fee. They cannot find a buyer fast enough, so they work every contact they have: other investors, real estate attorneys, title companies, auction platforms, anyone who might know a cash buyer at that price level. One or two people show up. The deal closes. Those people move to the top of the list for the next deal, because they already proved they could close.
The thing that does not get posted about is how slow it feels between deals. At the luxury tier, a qualifying property might come along two or three times a year, so the list gets built in long gaps: showing up at investment events, building relationships with estate attorneys and family offices, staying in rooms where cash buyers at the million-plus level actually are. That relationship work happens before there is any deal to show, which is probably why nobody posts about it. There is nothing to announce.
Your instinct to study the contract mechanics at this scale and carry them down is a reasonable one. The disposition logic, meaning how you find and qualify the person who actually buys, is the same whether the fee is $8,000 or $120,000. The luxury version just makes the cost of getting it wrong much more visible.
I am not certain how buyer list building differs across specific markets at the high end, so for real sourcing practices I would ask people who are active in that tier rather than take my description as the whole picture.
What draws you specifically to the disposition side? Is it the sequencing question, or something about how buyers at different price points behave differently?