Spam submissions are 100% increasing in recent months. They are getting more advanced. I have about 20+ international clients and sometimes it is incredibly difficult to narrow down where the spam is coming from.
If you're running advertising, they will typically target a specific keyword so it typically helps to test. (They are typically more human/less bots for ads).
If this is SEO/organic using a paid tool is typically the way to go. As Mika said, the tools + finding patterns typically makes it pretty hard.
This year no matter what we did I had a particular client that we simply could not find where the spam was coming from. He is a plastic surgeon so we adjusted the form and make the first selection in the drop down something he did NOT do/wasn't on the website:
• Brazilian Butt Lift
• Breast Augmentation
• Facelift
• etc etc.
The majority of the spam isn't going to take the time to change the drop down item (and he doesn't do that procedure), but real patients don't notice. His team simply filters out anything with the first drop down item and we use those submissions for negative audiences in ads/are starting to find patterns where they are submitted from.
Hope this helps!