I think it would he hard to have a general no go on classifieds as everyone's circumstances are different.
I agree there should definitely be no collection only items as this is irresponsible on that part of both seller and buyer.
Couriers have a responsibility to make sure they take precautions, which most seem to be. Any insurance issues will be down to the buyer and seller making sure they have appropriate cover.
I think it's important to try as much as possible to keep the economy going, to a lesser extent the second hand market has a smaller role to play, but a role none the less.
I guess in conclusion I'm saying it shouldn't stop. Just be sensible. I would be happy for admins to remove classified posts marked as collection only as its clearly ignoring government guidance.
Just my 2pence