Can I put affiliate links on my site without first testing the product or services?
Maybe the legal point depends on the country you are. But to me, you don't care. It's not a question about is it legal or not, it's a credibility question. If you suggest your visitor to buy something and if this thing is realy bad qualety you will receive bad feedback and bad visibility / seo.
It might help to read FTC's ".com Disclosures" guidelines document on affiliate links and what to keep in mind in terms of disclosures:
Note that you need to properly disclose your affiliate links in a prominent way: "clear and conspicuous".