The confusion arises because expertise makes the beginner level feel embarrassing to write. Explaining something basic reads, to you, as stating the obvious, and the instinct is to demonstrate depth instead. That instinct produces material your competitors admire and your customers skip.
The useful test is who is reading and why. A prospect is not evaluating whether you know more than other providers. They are trying to establish whether you understand their situation and whether you can explain it without making them feel stupid. Clarity accomplishes both, and technical depth accomplishes neither.
Write for somebody intelligent who lacks your context, which is the position nearly every customer occupies. They run a business, they make decisions, and they have no reason to know your terminology. Assuming intelligence and not assuming knowledge is the register that works, and it is different from writing simply.
Use their words rather than the industry's, because the gap between the two is where most professional writing loses people. If customers say their website is slow and the industry says the largest contentful paint is poor, the page should contain both, with theirs in the heading. That is not simplification, it is being findable.
Include the depth where it earns its place rather than removing it. The reasoning behind a recommendation, the exception where the general advice fails, and the specific detail from work you have actually done are what distinguish your explanation from a generic one. Those can sit below the plain answer rather than replacing it.
Consider that some audiences genuinely are expert, which is worth naming so the answer does not sound absolute. If you sell to specialists, to other providers, or into a technical field, writing at their level is correct and writing simply reads as condescension. The question is who buys rather than what feels appropriate.
Watch for the material that exists to impress rather than to help, which is recognisable. Jargon without explanation, claims of sophistication, and depth on subjects the reader did not ask about all serve the writer. The version that serves the reader answers the question they had.
Then check it on somebody outside your field before publishing. The point where they stop following is almost always a place where you skipped a step that felt too basic to state, and one reader is enough to find several. That test is more reliable than any judgement you can make about your own writing.
Provide both levels on the same page rather than choosing, which resolves the tension entirely. The plain answer near the top serves the person deciding, and the detail below serves the reader who wants it, and neither audience is excluded.
Watch who actually contacts you after reading, since that tells you which audience your material is reaching. A steady flow of enquiries from people who understood the piece is confirmation, and interest only from peers is a signal that the register is wrong.
Avoid apologising for explaining something, since phrases acknowledging that a point may be obvious signal that you were uncomfortable including it. State it plainly and let readers skip what they already know.
Define any term you cannot avoid at first use, briefly and in the same sentence, since that removes the barrier without interrupting a reader who already knew it.
Notice how you explain things in conversation, since the version you produce verbally for a customer is almost always clearer than the version you write. Recording yourself answering a question and transcribing it frequently produces better material than sitting down to write it.