You're not gonna get booted for it but I would limit the amount of information about his services as the information won't make the link any more valuable to search engines and you may just end up ranking for his targeted terms.

You might be better served by having a general real estate information site with decent link pages and trade with third parties from there (assuming the designer won't allow you to add link pages to the guys site).

Once you get it going real estate webmasters is a great place for finding relevant parners. They have a good core of knowledgable members.

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