Villager Profession?

Just use default vanilla gui and apply it

In trade you can get something like AIR

Make villagers spawn in villages with return conditions

like woodcreatures said, just make a new villager with the exact same texture and download the GUI from Google or .minecraft folder and use this: MCreator Tutorial: How to make NPC Trades | 2020.3 - YouTube

a workaround could be with commands, by summoning a Vanilla Villager with a custom trade Minecraft 1.16.4: How to make a custom villager trades - Bing video however I don't think this is a good option

Well.. you can make custom professions and trades for villagers, there is even registry for that.

This feature is going to be in MCreator in future.

But you can make it right now with coding.

I can explain this too you and even provide example(from my mod).

Sure, here: https://github.com/Frostygames0/Elemental-Amulets/blob/master/src/main/java/frostygames0/elementalamulets/init/ModVillagers.java

This is how to register villagers. Use register method in the constructor of your main class.

Also, anything lower than registerWandererTrades is not needed.

 To give your villager a working outfit: https://github.com/Frostygames0/Elemental-Amulets/tree/master/src/main/resources/assets/elementalamulets/textures/entity

Also a small note: if you copy the code, then the license of your mod should be GPL v3 or any compatible license and not “all rights reserved”

If you want it to return empty item then use ItemStack.EMPTY in BasicTrade's constructor instead of new ItemStack(Item instance).

Or you can create your own trade class. 

package me.betadv.better_vanilla;

import com.google.common.collect.ImmutableSet;
import net.minecraft.block.Blocks;
import net.minecraft.entity.merchant.villager.VillagerProfession;
import net.minecraft.item.ItemStack;
import net.minecraft.item.Items;
import net.minecraft.util.SoundEvents;
import net.minecraft.village.PointOfInterestType;
import net.minecraftforge.common.BasicTrade;
import net.minecraftforge.event.village.VillagerTradesEvent;
import net.minecraftforge.eventbus.api.IEventBus;
import net.minecraftforge.eventbus.api.SubscribeEvent;
import net.minecraftforge.fml.RegistryObject;
import net.minecraftforge.fml.common.Mod;
import net.minecraftforge.fml.javafmlmod.FMLJavaModLoadingContext;
import net.minecraftforge.registries.DeferredRegister;
import net.minecraftforge.registries.ForgeRegistries;

@Mod.EventBusSubscriber(modid = "YOUR_MOD_ID")
public class ScammerVillager {
    public static final DeferredRegister<VillagerProfession> PROFESSIONS = DeferredRegister.create(ForgeRegistries.PROFESSIONS, "YOUR_MOD_ID");
    public static final DeferredRegister<PointOfInterestType> POI_TYPES = DeferredRegister.create(ForgeRegistries.POI_TYPES, "YOUR_MOD_ID");

    public static final RegistryObject<PointOfInterestType> SCAMMER_POI = POI_TYPES.register("scammer",
            () -> new PointOfInterestType("scammer", PointOfInterestType.getBlockStates(Blocks.AIR), 1, 1));
    public static final RegistryObject<VillagerProfession> SCAMMER = PROFESSIONS.register("scammer",
            () -> new VillagerProfession("scammer", SCAMMER_POI.get(), ImmutableSet.of(), ImmutableSet.of(), SoundEvents.VILLAGER_NO));

    // PUT THIS METHOD IN YOUR MAIN CLASS CONSTRUCTOR(Method that has the name of main class) (It's called like your mod)
    public static void register() {
        IEventBus bus = FMLJavaModLoadingContext.get().getModEventBus();
        POI_TYPES.register(bus);
        PROFESSIONS.register(bus);
    }

    @SubscribeEvent
    public static void registerTrades(final VillagerTradesEvent event) {
        if(event.getType() == SCAMMER.get()) {
            event.getTrades().get(1).add(new BasicTrade(1, new ItemStack(Items.DIAMOND, 5), 10, 1, 1f));
            // EXAMPLE TRADE (price, Item, max amount of trades before the "recharge", xp villager gets, price multiplier)
        }
    }
}

1.Replace YOUR MOD ID with your mod id, also call your file as ScammerVillager

2.Call register method in your mod constructor like that: ScammerVillager.register()

3. That should be all

NP, if you have any questions just ask!