Villager don't unlock new trades

Trying to get a Villager market got some clerics. I traded some zombie flesh and gold for emeralds, but now i have already 3 useless clerics because they 3 are unable to trade and never leveled up.

Also, there is a point whit all villagers that they block the trade, giving back all the trade items, e.g. 40 zombie flesh AND 1 emerald