Give your client choices:

1. Pay the fee which includes extra protections shown in the wonderful brochure you will hand them https://proconnect.intuit.com/content/dam/intuit/pro_tax_group/en_us/docs/PBR-ID-protection.pdf
2. Pay me now and there is no extra fee Give them an idea of how long refunds SHOULD take https://www.cpapracticeadvisor.com/news/12370552/2018-irs-income-tax-refund-chart-when-will-i-get-my...
3. Send them to a VITA office and get the return done for FREE https://www.irs.gov/individuals/free-tax-return-preparation-for-you-by-volunteers
4. Direct them to the FREE IRS site https://www.irs.gov/filing/free-file-do-your-federal-taxes-for-free

Personally I would not try to "Explain" this fee. Add on another 10 or 20 dollars to it and offer the service. Everything you do with the client is negotiable, everything except kindness and concern for them as a person. Provide a great deal of that and you will get generations of clients.