We are an Odoo partner, so read this with that in mind. We have tried to write the list we would want a buyer to bring to any partner, ourselves included, and we have not answered the questions here on our own behalf.
None of the questions has a single correct answer. What matters is whether you get a clear answer, in writing, before you sign — and whether it matches what ends up in the contract.
Who they are
Odoo publishes a partner directory on its own website, searchable by country. Look the company up there yourself rather than relying on a logo in a presentation.
An ERP is an accounting system with other modules attached. A configuration that ignores how your books must be kept will be redone later.
A conversation with a past customer tells you more than a page of logos. Ask them what went wrong, and how it was handled.
You are buying the team, not the brand. When people change often, your project gets explained twice.
What you are buying
They are different products with different features and different costs. Neither is wrong, but you should know which one you are paying for.
If it is in the partner's name, changing partner later means asking their permission.
Ask who takes the backups, how often, and whether a restore has ever been tested.
Licences, hosting, customisation, migration, training and support are separate lines. A single figure with no breakdown tends to grow.
Custom code has to be carried through every upgrade. Standard configuration does not.
How they work
A written process document is the only thing you can later hold the configuration against.
Cleaning usually falls to the buyer, and it is easy to leave out of a quotation. Agree who does what before the price is fixed.
Training on a demonstration company teaches the menus. Training on your own items and customers teaches the job.
Ask to meet the consultant who will configure your system before you sign.
Each phase should end with something you can see and accept, not with a date passing.
A good answer is specific, written down, and the same the second time you ask. Be wary of any answer that is only a yes.
After go-live
The first month-end close on a new system is where problems tend to surface. Know who will be there for it.
Ask for this in the contract, not in the conversation.
Configuration notes, custom code and administrator access should be in your hands, not only in the partner's.
You should be able to leave with a full copy of the database and everything needed to run it elsewhere. Get that in writing while everyone is still on good terms.
Put the same questions to every partner you are considering and lay the written answers side by side. Differences in price usually trace back to differences in these answers — what is included, who does the data work, how much is custom. Then check that the contract says what the answers said. Where it does not, ask for it to be changed before you sign, not after.