To think this was a strange way of conducting market research?

This person should have showed you an ID card first and then said a little bit about what she wanted, perhaps it was a survey about how many people are switching to ALDI from other shops, it may also have been from a rival store (this often happens).

If she had an ID, it should say she is working for a MRS approved company and have the phone number on it so you can check.

It does sound dodgy as she was asking for your receipt.
Ive been in the business for 20 odd years and some surveys can be hard to understand but if in doubt then walk away.

She was standing right outside the main door, Nonu so I guess they must have known she was there. I didn't notice any ID but I did notice that nobody was passing over any till receipts.

My thoughts too Nonu

Merlot that seems slighty odd to me !

Just saying, did ALDI know and had she got ID on her ?

Perhaps I have a suspicious mind . Hey-ho

Your DH is a hoot merlot, isn't he?

But that's just not on at all - especially demanding your till receipt! Mind your own business, Missus!