Turnitin costs a fee to the educational institutions that use the online service, and it is not necessarily a reliable plagiarism detector, according to the company's website. Rather than specifically serving as a plagiarism detector, the tool looks for text that matches other content that has either been submitted to Turnitin or posted in journals or on the Web. Educational institutions can ask for a quote on the Turnitin website to find out how much the service would cost.
Since Turnitin finds matching text in students papers, it can be helpful for detecting possible plagiarism; however, not all matched text is necessarily plagiarized, so educators must determine what is or isn't plagiarism in an individual's paper. For example, a student might properly quote another source, and this would show up as a match; however, it's not plagiarism if cited correctly.
There are other reasons why Turnitin may not always be a reliable tool for checking plagiarism. Students can reword their papers to deceive the detector not to show matches while still committing plagiarism, warns WriteCheck.
There have also been controversy with the Turnitin service. Since students have to turn their papers into the service, some students might feel that they've been presumed to be guilty of plagiarism. There have also been concerns with student privacy regarding materials submitted to the database and student copyright laws.