Before I got my strips on prescription, I bought mine from Amazon and never had a problem. Now my GP has reduced my unlimited strips to just 50 a month, I went onto Ebay and bought a 'job lot' for my Accu Chek aviva and they are fine, no sign of any prescription sticker. I would just say watch the seller, read the feedback carefully and then make your choice. I just can't see the point in paying £25+ for 50 strips if you can get them cheaper. That said, I would be absolutely fuming if I got some strips that had initially been prescribed, and therefore they were being gained on script, for profit.
[edit to add] My first meter was an SD codefree, I found it read a little higher than my Accu Check.