Yes, the problem with permanent marker is that quite often, it isn't, particularly when used on tape. Taping over it is the least likely method of exceeding your weight limit, especially when you consider that a single A4 sheet of copy paper weighs in at an amazing 5 to 6 grams!

I have a set of calibration weights which I regularly use to check (and adjust if necessary) my postal scales, so if a DVD in a number 1 padded envelope weighs in at 125g, I know that I only need to put 2 stamps on it because the scales at my LPO will read exactly the same.

I had to pull them up once when their scales didn't agree with mine (only by 2g) but I was confident enough to tell them that their scales were incorrect, and when they weighed my item on a different set of scales, it showed that the first set was indeed out by 2g. Turned out that somebody had moved them and failed to readjust the levelling screws, and once done they were once again spot on.

It probably helped that I'm a regular and know them quite well, but they were actually very grateful that I'd pointed it out, as they could have got into a lot of trouble had it not been noticed. These days though, they no longer check my large letters or parcels as they know that the weights and dimensions (for cubing) that I write in pencil on the front is always 100% accurate.