I don't think ending commingling will stop that from happening, since Subscribe & Save is set to switch to a different seller with a lower price by default.

In the US, when Subscribe & Save is set up, it is set by default to receive orders from "Amazon.com and other top rated sellers". If you want to change it, you need to go into the Subscribe & Save page and change it to "Amazon.com only".

I've had an order where I initially placed a new subscription sold by Amazon.com, but a 3rd party seller would lower their price by a few cents, and Amazon would change the seller and I would receive grey market goods.

I haven't found a way to change the default for new subscriptions to always use the same seller that I set up the subscription with, so I need to manually change it for every single new subscription.

Thanks for this. I had no idea this was even a thing, and it explains some discrepancies I've seen with my one subscription.

They really don't make it obvious where to change it, either...