I don't know where kfbphoto got their info from but they are not wrong, however the rate of duty varies. [I should have said I can't comment on the practice of selling to a good friend of course]
(One of) my blog (s) comes up top of a google search for importing a vehicle into gib, and I did an update on the excise duty here. Unless things have changed, I give the varying rates of duty which are dependent on new or second hand vehicle, and engine size.
We imported our vehicle four years ago and DID need to produce a resident's card. However if that has changed it would be helpful to know, or how you managed without the card?
As for working as a part-time second-hand car dealer in Gibraltar - that's not exactly easy unless you live in Gib. It isn't that easy if you do. Either way you would need to register your business in Gibraltar.
I've answered these in reverse order, sorry about that, but there is no multi-quote (unless I have missed it).
As for shipping or driving down, we drove down. It's pretty easy, people do it all the time just for holidays.