1 sword hilt(common)
1 bug carapace(common)
1 gemsteel(rare)
= common item x 25, phoenix downs.


5 electrum(rare)
3 gemsteel(rare)
4 damascus steel(uncommon)
= Uber weapon X


Now you start to sell your gemsteel as you get it, along with the electrum and damascus steel.
You get bug carapace and sword hilt before finishing the full recipie for Uber weapon X

You sold 3 gemsteel, 4 electrum, 4 damascus steel, and then 1 bug carapace and 1 sword hilt.
The recipie for common item x 25 activates.

It wipes gemsteel bazaar counter to 0
You just lost 3 gemsteel and have to go farm them again.
Now you have 4 damascus steel, 4 electrum, and 0 gemsteel on your bazaar counter, so when you turn in that 5th electrum, without getting any more gemsteels, it gives you a nice nothing...

Also
Similar example

4 high arcana
3 serpent skin
2 gemsteel
= uber armor B

4 damascus steel
5 electrum
3 gemsteel
= Uber weapon X

You can sell the high arcana, serpent skin, electrum, and damascus steel. Then if you sell 3 gemsteels at the same time, without closing the window, you will trigger BOTH recipies..
However if you sold one gemsteel at a time, you would trigger uber armor B first, and reset the counter on gemsteels for uber weapon X.

When you complete a recipie(and exit the sell window back to the main vendor window), the counters for that recipie reset to 0

sell 99 damascus steel
15 electrum
3 gemsteel
10 wolf pelts

Bazaar gives you uber weapon X, resets counters to

0 damascus steel
0 electrum
0 gemsteel
10 wolf pelts(wasnt included in the recipie)

These arent actual recipies, hope this helps.