First off, I don't think this is exploitable, but it could definitely cause accidental purchases and frustrations for players.

By spam clicking on the pop-up that confirms buying another stable, I was able to buy 7 stables at once. It seems like the correct amount of money got charged, although the bank history is jumbled (it appears as if I'd first paid 15k, then 10k, and then 15k again per stable, but I counted and am pretty sure I got the right number of 10k and 15k stables). The same can be done with the DP stables, where mistakes are even more irritating.

You can see a screen recording here: https://imgur.com/a/bug-testing-LwOTDJU

The upper video shows the above process. The bottom video was from when I was almost out of HRC stables - found I at least couldn't cheat my way into getting additional HRC stables via multi-clicking, woop!