Since I have a lot of experience with this and deeper insight into the PK mentality, let me show you how to talk to PKs. Here is my 7 step program:
Above all, be prepared for this to be a longer journey. You can't expect instant gratification here but the outcome is well worth the effort!
1. Make sure you wear decent gear - providing PKs with good gear provides a favorable atmosphere and is a first step. The importance of step 1 can NOT be underestimated!
2. It helps not to selfres or get ressed elsewhere and trying to get your stuff before they are done looting - again, this will earn you credit.
3. Don't get upset when getting reskilled, it's actually their way of saying "we like you".
4. Compliment their PK abilities - it is important not to come across as being sarcastic here. Make an effort to compliment them and find particular points to compliment PKs individually. The best feeling for a PK is not only to kill but also to be recognized as an individual that stands out of the crowd!
These steps might require repetition depending on the PK(s) you're dealing with. Don't give up, rinse and repeat as needed!
Once all of these steps are completed it's time to move on to the next phase:
Don't try to get your stuff back while the event is still going or while the PKs are still busy killing people. You will ruin the great atmosphere you have just successfully built up by following steps 1-4. Wait until after the battle or event or at the very least until the PKs take a quick break. You don't want to appear as a nuisance to them or as getting in the way of their business.
5. Try offering to buy your gear back. Make sure you offer an ammount that is at the very least 50% of what your gear is actually worth - the higher, the more likely you will get your stuff back. Don't ask them to return it for free. Also make sure you don't come across as demanding. They are in control, make them feel accordingly.
6. For step 5 it may be better not to use general chat. Try approaching PKs individually and in person by meeting up with them. The PK mentality is all about being rough & tough and maintaining that reputation, especially among their peers. Any sign of weakness will immediately be exploited by the other inhabitants of the shark tank they're living in - they simply can't afford to show any kind of weakness, at least not in public and especially not in general chat.
It will help a great deal to repeat steps 1-4 with the individual PK to build trust.
7. After a while the PKs will feel sorry for you and you will notice that they start targeting other players over you, leave your items on your corpse or even give back your things for free. It is important not to push them though. Do not ask for this step to happen, it has to come naturally. The PK needs to have the feeling that this is their own idea and that they're still in total control of the situation.
I hope this helps. If you require further advice, you know where to find me.
PS: There are PKs who will offer to return items or not loot at all and even admit to it in general chat. These are usually the mentally strong and confident type who are not afraid to publicly show such weakness. You should worship these as demi-gods, they deserve it!
As for who is in UWSP, I have a scribe and my multi crafter, tailor, tinker, etc..
I wasn't necessarily asking for skills... What are your character's names? I would use their names to find out where that vendor is by using vendor search, so names are kinda important here.