Just to add to Jessica's response, I am also quite certain there is no issue with selling past applications. Written applications are your own work and therefore you have a (at least prima facie) right to do as you wish with them. As compared to information or materials you may have obtained during interviews or a VS, an application cannot be argued to be covered by any kind of confidentiality agreement. The only conceivable angle where the SRA could take issue with this would be around its 0-tolerance for dishonesty policies for character suitability assessments. However, since (i) platforms like the ones you have mentioned only advertise past applications as illustrative examples of what a good application should be (and not as something to copy and paste from); (ii) firms generally have effective automated systems to check plagiarism; (iii) access to past applications is quite widely available in university law society mentorship schemes; and (iv) wanting to access to model applications as a means to review one's own work is a legitimate motivation and stands to improve quality of application, I definitely think selling your applications would not be deemed as 'dishonest'.