To build a Messenger Bot that will do what you want it to, you must use a developer who knows what he is doing. There are many developers out there who claim to be able to build Bots for Messenger. Some of them are good, some of them are mediocre and some of them are not worth your time or effort. Here is a checklist for you to use when searching for a developer.
Does the developer have a working Facebook application? If they don't, chances are they don't know how to use the Facebook API. Instead of getting ripped off by a developer who doesn't understand what he is doing, I would recommend going with someone who has already built an application with the Facebook API.
Does the developer to use text-to-speech technology? You want to be able to hear your Messenger Bot on Facebook. If they don't have text-to-speech technology, you should move on to the next developer.
Do they give you an option to use a pre-written script in order to help you build your bot? If they don't, then move on to the next developer. Every bot needs to be custom made.
Does the developer take requests for new functions? If they don't, you need to find someone else.
Is the developer going to build your Facebook Chatbot for you? Building a Bot for you is essential because you want to be able to custom build your Bot in such a way that is compatible with your website.
Are the developers you have contacted after-hours? If you are not on a business night, you should assume that the next day will be the only time you will have to contact them. You want to be able to work with someone who can be reached during normal business hours.
Do they tell you where to send your bot? They are not going to tell you where to send your bot, but you need to know how to get it to send your messages.
How much does the Bot cost? Don't settle for a Bot that costs a lot of money.
What are the guidelines for getting your Bot approved? Are the guidelines similar to those of other applications? This means the Bot will be approved by Facebook within a few days of being submitted.
How long do the creators recommend that you allow your Bot to run before you start to receive spam? The creators will tell you when to expect to see any spam.
Is the Bot written in Java? In the past, most developers used C++, so if you plan on building a Bot, I recommend using Java.