I dont charge to do a review, but I do have a banner up that I charge for. I do not return samples, and occasionally will offer a contest for a product that I have not personally reviewed. When that is being the case, I simply review the website not the PRODUCT.
You should start off by reviewing things that you use or things you have just purchased. Make sure to write thorough reviews and before you know it, a company or PR firm will contact you to write reviews of their products.