I agree withal the above.
For a "BRAND NEW" client I will review (for free) several years previously filed - completed returns but if they need amended or "filed" it is standard cost.
I have had several non-clients wanting me to check their work; and two clients who wanted me to "check" their NEW preparer (new guy gave a GREAT price but...).
All were told I would happily check the work --- at the same price I would normally "do" their tax return preparation as the same work was involved in checking as was involved in "doing" original return.
Several walked away, one of my "old" clients said OK and did leave me for the "new guy", one client said OK and understood why the charge from the "new guy" was so low and came back to me.
If they want a "calculation check" with just numbers entered - perhaps a slightly less cost as it is just imputing numbers *** BUT *** if they want an opinion or anything other than a number check, why would I do that for less than normal fee? Bottom line ---- time and effort and our cost to do does NOT change if we are "checking" or "doing" the tax return - so fees stay the same.
Your choice, what is your time, expertise and more importantly your reputation worth?