This business, located in the warehouse district, is owned by a former adventurer named Chobham, who became a skilled armorer after he retired from active adventuring in 1148. These days, his business mostly makes armor of all types from leather to full plate, and also offers repair of non-magical field plate and full plate.
The business does, in addition, buy and sell magical armor, but generally only up to +3, as better items are usually sold at auction. They will pay 90% of Unearthed Arcana value for magical armor of most types.
Note that non-magical Field Plate and Full Plate must be 'sized' to fit the wearer, or it will not absorb damage. This will cost an additional amount over the amount listed. This requires the skill of a level 3 armorer, and cannot be done by simply polymorping the armor (unless the person casting the polymorph has the skills of a level 3 armorer).
Note that normal field plate will cost 5000 gp and take 4 months to make, and full plate costs 7800 gp and takes 6 months to make. There is a chance that they will have normal field or full plate in stock that is a close enough fit that it can be altered as above.