You've clearly had a bad experience, but
some of your criticisms aren't really fair. On the item under discussion, their website clearly states that there are 10 in a pack, and they have 4 packs in stock . . .
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On the postage question, I can understand that the postage (on orders under £40) seems high when you are buying only small items but, on the question of your aborted order for track, they clearly state that they have "
the right to charge a premium on large/oversize/overweight packages" and they clearly quoted you a cost for postage before you committed (or not in this case) to buy . . .
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You also have to remember that the delivery cost not only includes the postage fee, but also the cost of materials and (maybe) staff time.
I have made purchases from GRS over many years (but not so much recently, as I "have all I need"

) and the experience can be "a little variable", shall we say, but they do hold enormous stocks, they stock items not available elsewhere in the UK (as in this case?), produce their own items, and we'd all be worse off without them.
Maybe a forumite local to GRS might pop in for you, and post them on at cost. I'll let you know if I'm heading that way.
Cheers
David