There isn’t too much of an opportunity for sneaky stuff that a rouge would typically do in something like D and D. If they are going for the more swash buckling rouge type idea then perhaps the corsair archetype is what they are after.
There are also two kinds of mages: The ritualist and the mage. The mage then breaks down into the support mage and the battle mage and the ritualist breaks down into the ritualist and the arcane projectionist. Depending on what you go for will depend on what kind of game you will have. If you play the hakima archetype (magic users and scholars held in high esteemed) then your guard friend could go for the kohan archetype as they are known for serving the hakima.
If you are going to become a ritualist then you will need to know about the realms of magic. This side is more role play heavy but will mean you have fewer points for battle skills if you want to fight. It also has less immediate effects as you need to set things up and then sometimes wait for things to work.
Do you have a tent you are going to run the shop from or are you going to have a box you carry around to sell from. If you are going to be stationary then I recommend you contact profound decisions about getting a place to set up.
(I hope I’m not bombarding you with too much information, if I am, feel free to tell me to shut up, I can go on for hours so you can’t really wait for me to just stop unless I feel things have been concluded sufficiently enough that the other party, you in this case, is able to get on with the game without feeling they need to worry.)