We are required to tell you that there is no relationship or affiliation between the linked commercial organisations and the IMSLP / Petrucci Music Library beyond the links themselves (nor do we have any desire for there to be such a relationship). We are also in no way expressing or implying that these organizations support, sponsor, endorse, or contribute money to any charity or other cause. These are not paid advertisements. The IMSLP / Petrucci Music Library receives a commission only on items actually purchased from the linked organisation's website. Prices of linked items are determined solely by the selling organization and are not increased or changed in any way by access from this site.
For reasons why there must be commercial links on IMSLP, please read this forum post. There are also other donation methods that cut out the middleman, and allow you to donate directly to IMSLP.