Reject or Crack Your Head?

What do you do when you've accepted an offer to write a review on a topic that you have no idea what to write about or the subject is totally alien to you? Do you reject it or spend an hour cracking your head and praying for a brainwave? Well, if I have the time, I will do some google search on the product, then write about it. But most times, I'll rather be lying on the couch watching TV than crack my poor head. In times like this, I'll wait till the eleventh hour for the offer to expire and if I still have no brainwave, I'll reject the offer.