Be aware that if you place an online grocery order it's likely that you will not get a fair substitution if the deal has changed or the items are out of stock.
I ordered 2 packs of 24 cans of coke for £7.50 each
these were substituted for 2 packs of 18 cans at £9.50 each
Sainsbury issued a credit of £4.00 that can only be used online. Other supermarkets give an automatic instant refund…but then other supermarkets ( like Tesco) substitute for the same value or more NEVER less.
I received 12 less cans which is not compensated in the refund. On collection I asked the member of staff if this shortfall would be compensated and he assured me that it would. Other wise I would have refused to accept the substitution. When I complained the response was that I was sent an email shortly prior to the collection outlining the substitution and should have refused. I was out and did not check my emails - also I have never been shortchanged by other supermarkets so I wasn't expecting it now!