I am a bit wary about whether this is a thinly disguised legal advice question, and the forum that you've posted this in is pretty suspect as far as that goes. This should probably be moved to
European & African Drug Discussion or maybe
Drug Policy and Media Coverage at a stretch, since unless this was a genuine mistake, without actually saying it you're clearly wondering about importing PEDs that I suppose are not legal in your jurisdiction... however that's an issue for the current mods and I suppose your question is innocuous enough, if frustratingly vague, to give an equally vague but maybe somewhat useful or at least interesting answer.
Intra-EU shipping of anything is generally going to be very light-touch for anything that can be easily shipped my mail, the EU is a customs union so there is little reason for individual nations to do anything other than a light touch, there aren't going to be additional import taxes imposed on anything and that is the primary reason for cross-border shipping restrictions in the first place - to make sure people aren't avoiding taxes. We live in a capitalist world, the primary goal of every single law enforcement agency is to protect the interests of capital. If there's no prospect of protecting the capital of the government controlling the jurisdiction, because there can be no additional taxes collected, then it is simply a waste of capital to do anything else. There are some exceptions to this, but they are few and far between and not really even worth mentioning in this context, IMO... and they all circle back to protecting the interests of capital is more indirect ways, anyway. This is mostly true for nations outside the EU proper but within the customs union, too.
The EU really should be moving towards full federalization ASAP, in my view, if we wanna have a somewhat principled if flawed major power left to contain the ambitions of the US and China in this dark world that we're moving into, but that's a political discussion and nothing to do with what you asked.
Importing from outside the customs union is where individual nations' approaches become far more relevant because the first country in which a package lands is the country in which it's going to be most scrutinized, because this is the only point at which it's crossing a "real" "border" where laws and specifically taxation laws differ. It depends very much on the origin country, but sometimes moreso on the carrier.
Remembering again that the primary purpose of law enforcement agencies in a capitalist world is to protect the interests of capital, there are some carriers that are de-facto subject to less scrutiny than others, because even if the contents or the import tax are declared inaccurately, these carriers either play a large enough role in the local national economy that the risk of agitating them by delaying one or more of their packages for additional import checks is a greater financial risk to the local government than anything that might reasonably be collected in unpaid import tax, or they just have other more indirect arrangements set up which ultimately are about money changing hands between heads of business and people with political power, and jeopardizing these arrangements would be financially risky.
However this is where it varies a little more depending on the category of item being imported, too. A computer component that looks undervalued has a realistic prospect of recovering the unpaid import tax from the buyer. A dietary supplement that looks like it might be illegal does not. So, counterintuitively, although one of these is more likely to be being imported illegally, the other is more likely to be actually challenged - depending on the carrier and the country in which crossing the imaginary customs border actually takes place. HOWEVER, there's another layer of capitalistic calculation going on on the carrier side, in that some carriers will be far more careful about shipping "dietary supplements" to certain jurisdictions than others because their own international reach and economic footprint in certain jurisdictions will allow them to evade scrutiny more than in others. We're obviously talking about drugs here - but the same is true for other categories of product and other categories of shipping, and other categories of carrier, ie, a company that handles cross-customs-border shipping of industrial machinery and relies on government contracts in their primary country of residence will take far more care not to ship sanctioned weapons disguised as industrial machinery than one with no such contracts and without the capacity to handle certain categories of shipment.
So... there's a lot going on and I actually think it's quite an interesting conversation, and it is a shame in a way that we can only have it in a very abstract sense. But once you recognize that the primary function of border controls for shipped goods - and the primary function of law enforcement agencies in this capitalist world in general - is to protect the interests of capital, above and beyond any local or international laws, no matter what any business leader or politician might claim - it makes it a lot easier to understand what works and what doesn't, as far as international shipping of possibly controversial items goes, to put it as diplomatically as I can.
Obviously that's not something that directly translates into practical advice, although it's impossible to give any without it becoming legal advice, typically you acquire that through trial and error, depending on what laws you're intending to evade - in this hypothetical thought experiment - lol, sorry that's so fucking SWIMmy but I couldn't resist - but you can also find out by looking into the carriers likely to be shipping your item(s), and for the questions that you wouldn't want to ask them directly, you can ask forwarding companies that utilize multiple carriers and exist specifically to ship items to places that retailers don't want to ship directly, for whatever reason that might be. So by their very nature they are both far less exposed to risk themselves and usually far more willing to talk about what kind of contents declarations will be challenged or not, and what carriers are best for what items for what destination country - in my limited experience.
