First of all you need to be sure that you've got adequate contact information. It used to be an e-mail address was good enough so that you could start a business relationship but now you need to get some further point of contact like a telephone number, a snail mail address or even some kind of social media to look at like a Twitter or a Facebook page. The reasons for needing this much contact information are simple. It’s important that you can rest assured that you are dealing with a reputable company and on the Internet that means you’ll need to have several different points of contact.
Even then you want to be extremely careful when people start asking for free samples of your writing and one of the best ways to get around it is to have a comprehensive list of your past work on a website. Several times I’ve been asked to write samples and pointed perspective clients to my website where I've stored information away that highlights my experience and provides URLs and samples to my previous work.
One of the rules that I like to use is the fact that if you’ve been around for a while in the writing game and have a portfolio of your work there’s really no reason to provide anything for free. If you’re a proven writer with a background you should get paid for what you do even if you make a promise to rewrite according to your client's specifications for free so you can get on the same page.
There are several other things that you want to look out for when you’re writing for a living on the Internet and they include the promises that go along with free samples. Usually I found that companies who promise you a lot of work without being clear about payment methods can be the ones that you need to watch out for in the end. Sometimes the people who promise you the world aren't necessarily dishonest but they've just oversold the amount of work that they think they’ll be able to get.
Finally, I just like to remember that there’s never a contract with any freelance writing that I do on the Internet so there’s never any reason not to pay me for my time and effort because clients can let me go just as quickly as they hire me if they don’t find my writing is up to the standards they set. For me there’s no reason to give out any kind of free samples.