Cheryl,
I'm not sure what you mean when you say "how do I say no ( legally )".
It seems to me if you control your site, it's personal choice what you link to. It seems much like choosing ones friends. One can be dissuaded from certain folks but ultimately it is your choice.
Some time back I was approached by someone asking me to link to their page. The page in question did contain some general genealogical information but beyond that it was a commercial site. So I declined it.
Another one was for a DNA testing service. Thank you no.
One person in asking for a link pointed me to a page on my site, that I had inherited from another CC, a page of links. It was a page I hadn't visited in a long time. Previously only to fix broken links. I was not happy with what I found and started removing links from the page because it linked to several things that had nothing to do with the core mission of the site, from weather to political and social issues.
As far as Facebook pages are concerned, there are certain groups I do believe offer resources including contributors or volunteers.
For example there's a group New York genealogy or some similar name, that has about 15 thousand members. Questions are asked, advice or answers given, with those on the answer side replying with links to or images of the answers to said questions.
When I visit the group I rarely leave without learning about some previously unknown source.
I had a possible indexing of records available to do that would take too long to do myself. It seems the natural place to go for volunteers. That fell through when someone pointed to me where the work was already done.
To me, not a bad place to point visitors to. Like I said personal choice within reason.
Tim Stowell
MNGenWeb SC
NYGenWeb ASC