"All items guaranteed, refunds available for any errors. Cant resolve if no contact"

You are not adressing that buyer now, you are leaving a message for any potential future buyers. They want to know if there is a problem what will you do about it.

If item is new without tags how come you have a RRP?

Personally I dont sell anything as new unless its got tags. Often if tag is missings it may be a second (sometimes the case even with tags) and have things like hanging straps cut. Selling as preowned will overcome that, and I find does not affect value. I sell a lot of dresses and find whether new or preowned makes no difference to value. Stating new leaves you no margin for errors.

In fact if an item is obviously a new second with a minor flaw, I will remove tag and sell as preowned.