I had an issue with an iTunes purchase a while ago. What happened was that iTunes split up my purchases (which were all completed within 10 minutes) into 2 separate orders and billed them several days apart. None tracked, and when I had to send in receipts for a manual claim, they refused to award the Avios for the second order because I had't clicked through on that day. If I had randomly clicked through every day until I received the email invoice, then they'd probably have allowed it, but I didn't.

There are a few – take Argos for instance. You can have 1.57% at topcashback or 4 Avios / £1 which (using Raffles' valuation) are worth 3p.

I have a cash-/points-back reference chart which people are free to use. Green cells indicate the highest rate of return for each retailer, whilst blue indicates the highest for each cash-/points-back service. Some of the information might be out of date though, because I don't update it very often. At its most recent update, House of Fraser, M&S, John Lewis and Tesco Direct all had a better rate of return via Gate 365 than via topcashback, even accounting for the Clubcard conversion bonus.

One interesting feature of Gate 365 is that it guarantees Avios within 40 days, which could be useful if you need some to stop a larger pile expiring. In contrast, one of my recent purchases via topcashback is showing as payable in 16 weeks.