I realise this response is a little late but I thought I would add it incase anyone reads through this forum and is still interesed in the question. Academic Knowledge do pay their writers fairly, so long as the quality of work is up to standard etc. Their invoice period runs from the 15th of one month to the 15th of the next, if you complete your work between, say, the 15th January and the 15th of February then you will receive your invoice by 15th Feb. The actual payment will be made at the end of the month (Feb). In this way you can be waiting around some time for the funds, but in my experience they have always paid me fairly, and on time. In certain circumstances - such as if your work is submitted late then they may not pay you at all, which I think is fair really. If the work is substandard they will usually tell you to ammend it before they reduce any payment that is made.
My advice is only commit to the work if you are absolutely sure you can get it done on time and to a good enough standard, if not, you will find that you do not get paid for you time and you will end up feeling cheated.