I haven't seen used bottles being sold, the majority I've seen have been for Ruh Khus, so those bottles probably couldn't be used for anything else, but it's a very neat idea. They can also get very large, like 5 tola bottles and I think shipping them is an issue because they could easily be damaged.
I wonder if people are okay with adding blends which contain musk and ambergris in such bottles? There's a concept of "Artisan's Clay" which is the settled solids of musk and ambergris from macerations, and I've heard that's often reused, assuming the new blend is the same or close enough.
It is -or was- used. Ambergris and musk are too precious and rare not to be reused multiple times.
I recall this story :
In
"Nishwar al-Muhadara wa Akhbar al-Mudhakarah" (1/294):
He said to me: I used to buy her fine Dubaiqiyah clothes, which they called [95 B] "shoe clothes." This was because they were thick and cut to the size of made-to-order shoes. They would be coated with musk and melted amber, then solidified. Between every two layers of clothing, they would place a fragrant substance with a firm consistency. We would do this with many layers, wrapping some over others. Then, the edges would be sealed with something made from amber and glued until the whole thing became like one piece. The outer layer would be smooth and white, stitched around with silk. We would make for it a "shirk" (a type of decorative strap), all made of silk, like straps woven from leather, and it would be worn.
He said: The lady’s shoes were made from this material, and she wouldn’t wear a pair of shoes for more than ten days, or thereabouts, until they would wear out, disintegrate, and the equivalent of several dinars would be spent on their cost, only to be discarded. The servants, or others, would take them and extract the amber and musk from them, which alone would be worth a considerable amount of dinars.
and another one (from the same book):
An Example of Caliph Al-Muqtadir's Extravagance
Abu Al-Qasim Al-Juhani informed me:
Al-Muqtadir wanted to enjoy drinking in a garden filled with narcissus flowers, located in a small courtyard of one of his many palaces. Someone responsible for the garden said: "The way to strengthen this narcissus before the caliph drinks in its presence is to fertilize it a few days beforehand, so that it will flourish and become more beautiful."
But Al-Muqtadir responded: "Woe to you! You want to use dung for something that I plan to smell?"
The gardener said: "This is the usual practice for anything that we want to strengthen and enhance its growth."
Al-Muqtadir asked: "And what is the reason for that?"
The gardener replied: "The fertilizer nourishes and protects the plants, helping them grow and bloom."
Al-Muqtadir then said: "We shall nourish it without fertilizer!" He then ordered that an amount of musk, equivalent to the amount of fertilizer needed for the garden, be crushed and used as the fertilizer.
He spent the day and night drinking in the garden, and even drank there the next morning. When he finished, he ordered that the garden be looted.
The gardeners and servants descended upon the narcissus, uprooting the plants along with the soil to extract the musk, until the garden was completely barren.
A huge sum of money was spent on the cost of the musk (after it was extracted and sold).