Happy New Year, everyone!
I think most sensible parents will accept that there's a lot of smoke and mirrors when it comes to what constitutes 11+ prep. As @PreplexJ intimates, prep doesn't have to involve formal tutoring. Parental involvement /engagement in everything from logic puzzle books to reading with your DC at night and discussing the book in question to buying them some Bond / CGP VR / NVR practice books is arguably "prep".
Realistically, any parent who cares enough about their child's prospects in the 11+ to be on a MN thread about it - and, even more so, parents whose children sat the 11+ four years ago and are STILL on MN threads about the 11+ - will be invested in the process sufficiently to be doing prep (or have done prep in the past), whether that's paying for a tutor or extending their child's learning at home - through discussions or workbooks or extra bits of maths and English or online platforms like Atom or visits to museums / galleries etc etc. It's all extending a child's knowledge and giving them a better shot at 11+. Sure, those parents can say "We did no tutoring and still my child got into a top school" but that's not really an honest appraisal of the whole picture.
Personally, I'm not an advocate of formal 11+ tutoring for a whole host of reasons, and certainly not of extensive tutoring, both for the sake of the child's wellbeing through the process (no ten / eleven year olds should be being flogged) and for their future happiness (it's a legitimate argument that if a child needs two-three years of extensive tutoring to get into a school, it's not the right school for them). But it would be risible - and a downright lie - for me to say we're not doing prep with DD just because we're not using a tutor. DH and I are of the opinion that any vaguely intelligent parent with a smattering of time and initiative can help prep their child for the 11+, and from what I know of DD's school cohort, while plenty of parents claim they're "not tutoring" they're doing exactly the same as us. Parents doing extra work with their child - even if it's only the odd ten minutes here and there - is still tutoring.
If what @BonjourCrisette and others are saying is "you don't need to flog your child to get into top schools" I would completely advocate that. But equally, to suggest it's all or nothing - or that invested parents aren't "prepping" their child in a whole host of inconspicuous ways - is disingenuous.
At the end of the day, we all want our DCs to get into a good school, be happy and thrive. From everything I've ever read on Mumsnet, pretty much every child finds their place by the end of the process, whether or not it's exactly the place they - or their parents - anticipated at the outset. Hopefully, by being open and honest on threads like this (it's anonymous, after all!) we can help one another navigate our way through it all.