It's not an authorisation it's the full payment.
I returned a closed box 128gb 7+ in black at about 7.30/7.45 tonight ( I purchased 2 last night but only wanted one in the end). Thought it would have shown up tonight as doubt there was time for anyone in store to buy before closing. No sign as I was refreshing at 10pm to see if any JB's! Maybe it will up show up at 6am for reservation.
Took over 2 hours in store tonight to exchange. Waited over an hour to get served even though had slot but because I bought original on the payment plan and wanted to refund the one I bought online last night and exchange for the one the payment plan it was all a bit of a faff! And not quite as straight forward or quick as I thought it might be. I had to do a whole credit application again (that part was quite quick but I was concerned that Barclays might not like 2 applications so close to each other). Anyway all done and am happy to have a black 7+. Think I would have regretted keeping the gold.
Next year I'll just stick on my 0% credit card for a couple of months. I think its easier for exchanges!