Boy, this is a general question. It really depends!
1 - what is your site about? It is most probably a commercial site and you are selling sth, you said?
2 - what are the links you refer to and how many are they?
3 - it always depends on the design, how do you present yourself and how do you present the links? Do you only put text links or also images? Are there animations or sounds (these are a no-go)
4 - where are they placed? Are the links in the focus for the user or only to fill empty space and only very observative users will recognize them?
Even the most suitable sites to be linked could harm imo if the design and presentation is crappy...
However, ask yourself the question: how do those links help you? What benefits do the users get from them? Then decide if it's worth it...