Never trust a tax preparer who fills out returns in marker
I got a couple of those today (by the same guy) and they were full of errors. One retired couple is getting a much bigger refund check than they thought, but another unfortunate taxpayer is getting a letter asking them to fill out some supporting forms. As a general rule, always carefully read your tax forms, and if you're putting a dollar amount on a line where the description tells you to attach a supporting form, fill out and attach said form or you will in all probability get a letter from the IRS asking for it later.
Never seen (or heard from someone who has seen) a tax return filled out in crayon, though.