When you're a freelance writer for hire (like I am) you have to find jobs to write for other people who pay you to do so. These people are called clients. Before you obtain a client, you should be aware of what they are -- and what they're not.
Your client is the source of your income. As in, this person pays you to work for them. That doesn't make the client your boss -- as a freelancer, you are the boss -- but signing a contract with your client makes you responsible to work for them until you deliver what you promised in exchange for the payment they promised. If this goes well for both of you, your client may offer you more work. If not, you'll have to find another client.
You know you've done a good job for your client when they pay you. If you do a great job, they will probably offer you more work. If you and your client work together well, and you're consistent with delivering excellent work on time according to their specs, they will likely want you to work for them on a regular/ongoing basis. Building a list of clients who offer you regular work and decent pay is the ideal situation for most freelancers, because eventually you don't have to go out looking for work anymore. About two-thirds of my clients have become regulars over the last year, and have already offered me jobs for the first half of 2016 and the holidays this year. That means I only need one or two more jobs for fall and I'm employed until 2017. I can also plan out my income for the entire year.
Be willing to negotiate with any client, and keep in mind that they're probably not millionaires with truckloads of cash to shower over you. Often unhappy ghost writers say that all clients are making tons of money while paying them pennies, which really perplexes me. First, why would you take a job that only pays pennies? Go for the better offers. Also, while I don't recommend working for pennies, there are some exceptions to that rule. If it's a trial job that the client is offering to see how you'll work together, and offers to pay more on future projects should you be a good fit, that's one. Another is if you have no prior experience. Being willing to work for a low rate may be the only way to get your first ghost writing gigs, but you can build on them. Once you have an established resume better-paying clients will be more inclined to hire you.
It's in your best interests to be picky about with whom and on what you work, too. When I started out, I decided from the beginning to be very selective, and only work for fellow professionals on projects that I would be happy to publish under my own byline. This results in excellent working relationships, invests me in the projects, and keeps the job from becoming a thankless grind. Also, if I'm ever accidentally revealed to be the ghost writer of any WFH project I've done, I'll never feel embarrassed.
When you have a problem with a client, my advice is to think before you pick a fight. The client didn't hire you to argue with them, snipe at them or give them any grief. It can be frustrating, especially when they change their mind about something in mid-project that requires you to do more work, but being nasty with them about it almost guarantees you won't receive another job offer. On the flip side, if the client is an ass, you can choose never to work with them again.
On rare occasions you may have a serious problem with a client. I always try to discuss it first, but some clients are simply problematic. My advice is to finish and deliver all work due, collect your payment, and then politely refuse any new offers. If you can't hang in long enough to finish the job, refund whatever payments they've made, thank them for the opportunity to work with them, and then politely refuse any new offers. The keywords here are polite and refuse. Whatever the situation with a client, always be courteous (even when they're not.) Also, it's better for you to refuse more work than to continue working in a problematic situation. You may be tempted to vent your spleen somewhere public about your negative experience, but given how obsessed people are with Googling themselves, they'll probably find it. All it takes is one disgruntled client to ruin a freelancer's rep. Write about whatever is burning your butt in your personal home journal, and then move on.
If you work through a freelancer site you can leave a negative review for a problematic client, but there may be backlash from the client that can get you bounced or banned. Also, future clients may see those scathing words and go hire someone else who leaves only good reviews for their clients. If your client clearly violates the terms of service at your work site, you can report them to site management, but they can just open a new account under another name and come after you. Bottom line, always think carefully before you play client police.
On the opposite end of the WFH spectrum, networking and client karma are wonderful things, and it's a good idea to cultivate both. Get to know other ghost writers and help each other when you can. I constantly refer good listings that aren't right for me to other ghost writer pals. I also try to help clients find a ghost writer when I can't do the job. For example, I had a publisher client contact me about writing a fairly large series project under a very tight deadline. I would have loved the work, but since my schedule was already full I had to turn down the offer. In my refusal e-mail I also recommended another ghost writer I knew who would be perfect for the job (and I did check with the ghost writer first before I mentioned them.) My pal got the job and was quite grateful, and the publisher thanked me for helping out. Later that publisher referred another client to me, so in the end I got a job out of it, too. When clients and ghost writers network like this, everyone wins.