If your wondering about why you might have got charged on your parcel even though it's marked as a gift and a low value some possibilities come to mind.
1) It was sent from a company and had a company name, stamp, address label or other identifier (like branded tape or box)
2) Things need to be person to person to qualify as a gift so from Joe blogg to fred blogs not plastic crack inc to Freg Bloggs. (so to speak).
If someone was to ask for something to be marked a certain way those are things to bare in mind - 'Person to person', 'Plain Packaging', 'Low value' & as a 'Gift'.
You can also have an exclusion on merchandise but the rate on that is for very low values (it's only £15.00) so it's pretty useless really you can barely Buy a CD with that. and they still try it on by saying that value can include the cost of the postage (which is pretty criminal in my view).