This is true. I believe writers should take pains to guide the students they work for and care about how the model papers are used
I usually just ask all of my new clients whether they want me to write their projects at the highest possible level or to hold back a bit and provide something written more at the level of a typical undergraduate. Sometimes, obviously ESL students ask me to provide work at the highest possible level, in which case I ask them whether they just want a high-level analysis but expressed in simpler English in terms of vocabulary and sentence structure.
Sometimes, even students whose emails exhibit quite poor ESL-English tell me that they still want the highest possible level, both in terms of substantive content and in terms of the writing. I assume that my (adult) clients know what they want and that they'll ask me for whatever best suits their intended use of my work; but I always alert them to potential concerns that they might want to consider. After I let them know that I can provide higher or lower substantive analyses and/or higher or lower levels of writing, it's up to them to ask for what they need from me.
After all, it will not serve the student a purpose if I write or wrote the perfect paper for him but he was caught using the paper dishonestly and he was removed from school because of it.
In 20+ years of doing this, I've had only one client ever report that he encountered a problem along those lines. This particular client's emails were written in relatively low-level ESL English. However, and for whatever reason, he specifically asked me to provide my very best work for the substantive content AND for the writing. Subsequently, he started bombarding my inbox with "EMERGENCY" emails about how his adviser had asked him some questions about the dissertation proposal that I wrote for him. When he couldn't answer those (very basic) questions, the adviser asked where he got the ideas for his proposal and who wrote it, and he responded that "an American friend" of his helped him. He ended up ordering a new proposal on a totally different topic; and this time, he took my advice to allow me to write it at a much lower level in every respect. That proposal was accepted, as was the eventual dissertation on that topic.
If new clients provide me with their own essays, I always caution them against ever trying to submit anything written by me for the same course in which they've already submitted any of their own writing, especially if their own essays are really bad. Sometimes they'll ask me to try to "match" their own level and just shoot for a low B or C; other times, they'll thank me for my warning and decide not to use me for that particular course, at all. Once in a while, they send me such bad essays of their own that I have to tell them that I just cannot "match" that level of work. In those cases, I'll offer to write the worst essay that I'm comfortable writing, with the understanding that they should rewrite it in their own style; but I still make very clear that the worst essay that I'm comfortable writing will still be suspiciously good if compared with their own essays.