I would do:
1) Check the reputation of the publisher.
2) Check where the publisher company is established? It that in a legit country or do they are in a tax heaven or even worse in a country where they don't care about copyright laws? In that government don't punish people for stealing from others, you can spend millions of dollars in lawyers and nothing would change.
3) Contact other developers that have used that publisher and ask about their experience.
Other things important to keep in mind:
- In general in life, if you were the one asking them for help it's less likely that they trick you compared to the ones reaching you out asking if you want to use their services.
- Having shared the development of your game for years, if popular, that could give you a little advantage since if someone steals your project, fan would know about it and they will help you spreading the voice and helping in boycotting the game.
All good points :).
I especially like that last one. Regular YouTube(and other community platforms such as GameJolt) content uploads during development, and building a website along the way, not only builds a community around your game, but all act as evidence that it is your work.
I wish you all the best in your endeavors, gametime777. Sit down with any publisher and just talk for a while(figuratively speaking. It will mostly be done via email, and/or instant messaging, etc. Get to know them as a company. See games/developers they have worked with. Talk to those developers, and get their point of view, and get an idea on how things went for them while working with the publisher.
Overall, you will get many different opinions, and viewpoints here, or at any community. All you can really do is speak directly with publisher(s), and developers who work wit them. Gather as much information as you can, in order to make the best informed decision on whether or not to work with them or not.