How to prevent having prospective students use me for free help, and then ghost me to go to another university In many countries there are funding sources that enable students or postdocs go study or work at a university of their choice, usually abroad. Usually for these applications, the applicant has to get in touch with a potential supervisor to get a letter of invitation and approve their research statement. More often than not, the potential supervisor is expected to discuss the ideas in detail, and also help improving the cover letter and research statement, since the award of the fellowship depends on it.

I have noticed the following situation recently: students from abroad approach me with interest to do research in my lab, and ask for help in checking their application and aligning ideas to my research. We have a call or two, we discuss the details, we come up with a strong application (that looks much better than the one they initially approached me with). As the application deadline approaches I don't hear back from them anymore nor they respond to emails.
Soon I learn that in parallel they approach a more famous lab with a much better application (thanks to me). Since the cover letter and research statement are now of high quality (for someone at that stage in their career), they are accepted easily, and get funding (sometimes directly from the lab).

This is new to me, and in just a short period of time I had three similar cases. I spent at least a day on each (calls, emails and checking the application), so it is a waste of time, and frustrating.

Is this a new trend? What is the best way to avoid this, while not discouraging genuine applicants?
A student contacts you and expresses an interest to work with you on your research. The student has funding contingent on your letter of acceptance and your approval of their research statement.

Ask the student to prepare a research statement. Tell him/her that you will provide all the necessary resources but that you will not write the statement for them or pre-grade it before it is to be submitted. Point them to the resources about your research, including Web pages, journal articles, and presentation abstracts. Provide them with a template research statement for a research project entirely unrelated to your field yet fully complete to be accepted in the other field. For example, when you are in a biology department doing research on gene expression, have a colleague in the physics department draft a statement on quantum dot fluorescence that he/she would accept as a suitable application. Alternatively, prepare a well-written application to a ballet theater group that expresses an interest to be Juliet in the upcoming production of Romeo and Juliet.

After that, let it be.

After all, do you really want/need to employ PhD students or postdocs who cannot initiate efforts on their own to prepare a coherent statement of their interest in your research?