The cost risk is spending on credential evaluations, translations, or TN-specific legal work that turns out to be inapplicable if the applicant does not hold qualifying citizenship. That spending does not necessarily transfer to a different immigration route.
Sequence spending after the citizenship answer
Ask any professional involved to confirm citizenship eligibility first, before quoting or beginning work on TN-specific document preparation. If a different route turns out to be necessary, that route will likely have its own document requirements, so early TN-specific spending may need to be repeated rather than reused. Confirm current government fees only once a specific route is actually chosen.
Ask any professional involved to confirm citizenship eligibility before quoting or starting work, and make that a condition of the engagement rather than a hope. The spending at risk here is credential evaluation, translation, and route-specific legal work, none of which necessarily carries over if a different category turns out to be necessary, since each route has its own document requirements. Where a second route is likely, ask what its preparation would cost so the household can compare rather than discover.
Confirm current government fees only once a specific route is actually chosen, since quoting them earlier attaches a number to a plan that may never proceed. Keep the two quotations separate.