The chance is low.
Honestly, I didn't see anyone being checked because they had a helium tank.
But this may be due to the fact that I have little interest in this topic.
People purchasing SN are also currently not checked (probably).
There was "only" a certain moment when people who bought SN were checked.
It was related to one source that was targeted by the services.
For example, I had no control because I was buying from another source.
Also, not everyone had control (if I'm not mistaken), even if they bought from this burned source.
Ropes, knives, etc. then there is absolutely nothing to be afraid of.
These are common items.
Why would anyone be interested in this?
Medicines are another matter, but also in most cases nothing to worry about.
It all depends on what paints you buy, where and how.
For example, I bought Domperidone through a certain website.
I got the recipe by taking a quiz on the website.
Domperidone came without any problem and I had no control.
If you're not being watched for any reason, you're not bragging to anyone about your plans and what you're buying, and you're not terribly unlucky, then you have nothing to worry about.