I am going to difer from the crowd and say I have had a good experience with freelancer.com. It is a legit website that won't steal your money.
The issue for many, though, is they pick bad freelancers and they get scammed.
It is important to vet your freelancers from the start. Research, ask them questions. Use the milestones. If the work is shoddy, you don't have to pay them, which seems dodgy for freelancers - but its great from a buying perspective.
To understand why I had a good experience on freelancer, you have to understand how I came into it. If I posted a project saying "I want a #1 position for X website for X keyword", you are going to get a lot of people from India posting who will be super cheap. But a lot of them will be scammers, whose work quality will be very low. This is very bad. You do not want this.
I went on to freelancer.com, armed in hand with a list of tasks I DIRECTLY wanted to have achieved. I had list of EXPLICIT, and when I say explicit, I mean incredibly explicit instructions. Step-by-step to the max. I provided the articles, I provided the proxies and I provided the email accounts. I then found a TEAM that had a leader that spoke excellent english, and I vetted them. Met on skype, chatted, sent through documents, we discussed them and I made changes to make it easier.
I have been working with this team over multiple projects, and I have been modifying my documents based off the results. I have achieved excellent rankings with them and I am very happy. It is a learning process. I asked for web 2.0's, and they would sometimes use wiki's that were terrible quality and would lead to dead links. And so I then modified my instructions explicitly stating to not use these, and we have been running away laughing ever since. We came across issues with social bookmarking, and so I modified that too. Things like this. I check the work, and I chat with the team leader regularly.
Because I know and understand what is going on, I can vet our team. By using freelancer.com I am able to pay them in milestones and they appreciate the reviews.
It is all about how you go into it. If you need pre-prepared packages my recommendation is the BST section, that is the best and I use it a lot in conjunction with my team.