The perfectly round "O" was the giveaway for me. Helvetica just feels more "literal" to me, if that makes any sense, with its perfectly horizontal endings on "C" and "S" and "t", so the round "O" seemed more likely. Mattel nearly tripped me up too, but I noticed that Helvetica was bolder throughout than the Arial equivalent, so it wasn't hard.
O isn't perfectly round in Helvetica. The Toyota logo is modified to use perfect circles for the Os. The real O is a bit rounder than in Arial maybe, but still not a circle. Futura is the one with the perfect circles (for both O and o).
I used the same rational. Whichever font looked bolder, I choose and got it correct. Also, the Staples Arial version didn't have the "registered" mark so I got that one easily.
But in the Mattel example, Helvetica is the thinner font. Instead notice the varying letter width, the M being wider than the A with Helvetica in the Mattel example.
