Transponders in Brava/o Marea are manufactured by Temic (now Atmel) and are supplied pre-programmed amd fixed code (not re-programmable).
Punto are Marin EM4102 and are pre-programmed and fixed So it is possible to buy the transponders and put them in any key. Thats what Fiat do. Thats also why Fiat cant program a key, because their specification is for a fixed key.
Its also possible to get a programmable transponder, think up a 32 bit code, run it through a calculation, and produce a final code to go into transponder. This transponder then will behave exactly like a genuine Temic or Marin key.
I use part of this last system to reproduce working keys, but I get the required code from the immobiliser for lost key situations.
The local market guy has probably got a genuine key and just copies it onto a new programmable key, and He's not doubt done dozens the same. Remember that the security of the system is the fact that ALL genuine keys have a different code.