If I understand correctly as long as the breed of dog isn’t considered vicious then owning it would be okay but not ideal, But would one be allowed to sell a dog/puppy and benefit from its sale?
There are 2 issues with selling dogs.
- The proceeds from the sale of a dog may not be used to buy sacrifices. As it says in Devarim 23:19:
לֹא־תָבִיא אֶתְנַן זוֹנָה וּמְחִיר כֶּלֶב בֵּית יְהוָה אֱלֹהֶיךָ לְכָל־נֶדֶר כִּי תוֹעֲבַת יְהוָה אֱלֹהֶיךָ גַּם־שְׁנֵיהֶם׃
You shall not bring the fee of a whore nor the pay of a dog into the house of the LORD your Gcd in fulfillment of any vow, for both are abhorrent to the LORD your Gcd.
Selling a puppy is no different to selling any other size dog.
- One may not own a dangerous dog, as discussed in the Talmud (e.g. Bava Kama 46a) unless one ensures it will not endanger or scare people.
One could argue that a puppy is not dangerous and most people are not scared of puppies, so it shouldn't be a problem to buy one, hence permissible to sell one.
The fact that eventually it will grow into a full-sized dog shouldn't affect the sale, and one can assume that the buyer will ensure that it won't endanger or scare people.
See here (Hebrew) for a list of halachic ruling concerning dogs, puppies and selling them.
That said, if the puppy is being bought for recreational purposes, it's not ideal, whereas if it's being sold for security-related issues, it seems to be perfectly ok.