A voluntary 5% donation seems quite acceptable especially when one considers that the item is generally seen by a dedicated audience and sale is quite likely, I estimate about 175 entries so far this year in the For Sale lists and most items eventually change hands, so over the course of a year should raise a few £s. As Henry Ford said 'there's no such thing as a free lunch' and while we all pay one way and another for our use of internet sites, this Forum is free to us as readers and contributors while there are many that require a membership fee to read/use the main content of the site or are blighted by advertising banners and videos. If it came to the crunch, I for one would rather pay a small annual fee than have funding advertisements popping up all over the place.
Trevor