Always use a reputable company, one that has been operating for at least five years or more. Referrals are the best, get someone you know and trust to refer you to a good operator in your area.
A good operator has all the bases covered, but sometimes delays are inevitable, for example, removing a slab of concrete may reveal underground plumbing. These pipes would have to be re-routed, which would result in a delay and additional costs.
A change in plans would only come from the client themselves – ensure you have a clear idea of what you want prior to starting.
Mess is inevitable, however, needs to be managed by your contractor. The site should be kept clean and tidy at all times.