Trying to think up a system to make handling trades for SL upgrading scrolls (A/G/S/XPro) safer for everyone involved. With the amount of scams as of late, I think this would be a welcomed addition for all parties.
Utilizing personal houses I think would make the most sense for this. Have an NPC that is available for purchase (just like all the others are), that allows you to upgrade within your house. From there, you can add scrolls to it (A/G/S/Xpro) that will then automatically be consumed when upgrading. Whether its 1 NPC with all of them or multiple NPCs for their corresponding upgrade (similar to the Pet Trainers)
When someone visits your house, they can interact with your upgrade NPC and see the scrolls that are available for use. They will select how many they wish to use, and then add their item, materials (erons, dice, etc...) and then upgrade.
To collect the payment, the owner of the House/NPC can interact with their NPC and select some sort of "Collect" option.
Again, this is a rough outline of the idea, but I think something along these lines can really help since you won't need to worry about collateral, trading items, etc... There is also a startup and maintenance cost (buying a house and the NPC) in order to have a "business" like this running.