@nate38You can haggle with shopkeepers to get lower prices. But it only works if your strength is higher than the stage number. (If it isn't prices go UP)
@Mr_MustacheYeah that's how you do it on the NES. According to the E-Manual with KI 3D you just had to hit A+Start whilst on the shop screen. But it wasn't working for me. Either:
- It doesn't work for certain shops (the black market ones?)
- Or I wasn't waiting until the shopkeeper had finished talking (although I'm pretty sure I must have done).
Anyway I did get it working, it's GREAT in the fortress stages if you're strong enough. You can go back again and again for low low prices.
Also another great tip I found at
Kid Icarus Code Shrine for the Treasure Rooms (the ones with all the pots):

For stages 1 & 3 break pots 1, 2 & 8. For stage 2 break pots 2, 6, and 7.
Then check the number of mallets revealed. The number will tell you exactly which pot the God of Poverty is hiding in! Avoid!
Stages 1/3: Three mallets= pot 5. Two mallets= pot 7, One mallet = pot 6. No mallets= pot 4
Stage 2: Three mallets= pot 1. Two mallets= pot 5, One mallet = pot 3. No mallets= pot 8