We've a link on a good, PR4 well established site and it's one way. I would however like to invite the owner of this site to write a guest post for us - not for any other reason than I am passionate about his core subject and it would work for our audience. Naturally it would only be polite to link his post back to his site.

Questions:

1. If we linked his post back would that then cancel out the good link we have on his ?
2. Do reciprocal links have any value at all in Google?