My husb goes with me most often. He's great about following all guidelines, and sometimes even reminds me that I have to do something obscure that I forgot about like "making note of what the background music is." I usually tune out background music, so he's great for that; and he's great with heights, weights, approx ages, remembering if someone had on glasses or not, and what they were wearing.
So...he's a fantastic co shopper
I have also taken any number of my kids when allowed. My 13 year old son is GREAT with details. He gets descriptions and names like no other. He will text them to me, pretending he's being a sullen teen playing on his cell phone. My daughter, who is 16, wants to shop when she's 18, so she's very conscientious about what I have to do...and she sticks around and sees reports being completed, too, so she knows Sassie vs Prophet, for example...
My son who is almost 18 goes for the enjoyment and doesn't do much to help out, but he also doesn't blab or mess anything up.
I have a six year old who has to be strongly admonished to keep his mouth shut. But he understands that we get to do a lot of these things BECAUSE Mommy works for it; and we wouldn't be going to movies, eating out, going to amusements...nearly as often if I couldn't work for it.
An interesting side note: Once when my now 13 year old son went on a shop with my husband and I...it was a shop for men's suits. My husb had to get fitted for a suit and I had to observe and do the report. We said that it was for my brother's wedding. My then (about 5 or 6 year old) blurted out, "But we just got back from Uncle Shane's wedding!!" He also once blurted out that I was on a mystery shop. So there were a couple snafus, but now he's great to go with....