Here is a list of the basic requirements necessary to provide a decent Odoo ERP implementation. My advice is: if the potential candidates cannot comply with these basic requirements, just run away: that will save you a lot of trouble.
Must have a solid knowledge in Linux and Debian systems deployment, administration and maintainance.
Must be familiar with PostgreSQL environment and engine maintainance and optimization.
Has a solid knowledge on accounting principles, Financial reports, Tax rules and account types.
Understands the business process and rules of Purchasing, Sales, Warehousing, HR, asset management and production.
Must be capable of providing a full first level Gap of Analysis before schedule or pricing can be made.