Do you allow people to advertise their site on your site?
What I actually mean is posting links with offers on your site, including free and paid posts.
If yes, how can it affect to your site?
Yes I do allow people to advertise on my website but not for free But i don't accept more then 1 backlink. External llow quality inks affects website. Its also affect link influence score sometimes, but when you are linking few authority sites it will not affect much and Content should look like natural not like promotional this is how i manage paid post.
I allow blog comments on my blog advertising their own websites. I personally do not offer paid advertising services or banner ads on my website. They keep my website much clean from link farms and makes the loading time much faster.