Offended! What would you do?

I would not be offended by being asked if I had the money when purchasing something, is a monetary transaction, so par for the course. Also in my experience there is never a receipt or a guarantee when buying second hand from someone’s address. She was being a pain imho.
Honestly, some people.

Please don't give it another thought she was offended over nothing thats her problem.
I certainly wouldn't sign anything reguarding faults its second hand if she wanted that sort of guarantee she should have brought new.

I'd have just left it out in the front yard on the boundary with the street.
It'd be gone by the next day.
No further involvement.
Not worth the hassle of selling things for me.
Just want to get rid of them.
Also I think money is much over rated.
I prefer an easier life.

Anyway OP don't let the incident worry you.
You could have charged her for your labour so she got off lightly.
Cheeky plucker.
As they - almost- say on MN.

I can understand why your DH checked about the money.

If I were buying something, I would say, ‘And it was £50, that’s right, isn’t it?’, before we had started loading it in the car.

Also don’t think it right to ask to sign saying ‘no faults’, as you buy as seen in that situation, I imagine.

"Nowt as queer as folk" or so they say! Don't quite understand the 'cultural' thing? I thought the British were well known for being reserved, happy to stand in line and loving animals

She, probably, had every intention of paying but how could you know that?
She may have been making sure she had help getting the cooker into the car before paying.

People seem to be so quick to be offended these days. You went over and beyond with your help and understand and you were perfectly reasonable to ask me the money. If this woman was offended, it was her problem, not yours. I would chalk it up to experience try and forget about it.

Oh dear. From the sound of it the woman was upset at feeling that you were suggesting she might be dishonest, and you are upset that you have offended her. Just one of those things, probably.

I'm nos sure what you mean by 'a cultural thing', and doubt that anyone likes to take offence. Maybe she was having a bad day, and your comment just touched a raw nerve.

Try not to be upset. It was just a misunderstanding, I'm sure

The professionally offended are out in force, it seems.

If she had not offered, I would have asked for payment before even helping to load. What a cheek to be offended for being asked to pay! Not worth thinking about an extremely rude person

Oh dear, that sounds very awkward. If you sell anything in future, ask for money upfront into your bank account.