I've found the source of a problem I have, and I think it's a bug.
I have this:
 
{
  "tiers": [
    {
      "total_exp_required": 0,
      "groups": [
        {
          "num_to_select": 1,
          "trades": [
            {
              "wants": [
                {                   "item": "minecraft:rotten_flesh",                   "quantity": 14                 }
              ],
              "gives": [
                {
                  "item": "minecraft:diamond_sword",
                  "functions": [
                    {
                      "function": "enchant_with_levels",
                      "treasure": true,
                      "levels": {                         "min": 10,                         "max": 10                       }
                    }
                  ]
                }
              ],
              "trader_exp": 30,
              "max_uses": 1,
              "reward_exp": true
            }
          ]
        }
      ]
    }
  ]
}
 
And it turns out that if I specify for example the value 10 for both the "min" and the "max", then the entity asks me for 14 + 10 = 24 rotten_flesh; and specifying the value 100 (in "min" and "max") then the entity asks me for 64 rotten_flesh.
 
That's, the wanted item quantity is added to the amount of enchanting levels used. I think that's not the way it should work.