Waterworks

This will be answered when you ask if all employees are licensed. The only way to obtain a legitimate tradesman's license is to be a legal or naturalized citizen of the US. The company may employ people in positions that don't require a license, however, so it's wise to inquire.

This is very important, since an estimate is just that. Many contractors will submit a "paper estimate", meaning they've written the estimate down on paper. The bill is the true amount owed and will almost always say "Invoice" or "Bill" at the top of the page. The bill should also list the date it was issued, the due date of payment, and a list of services rendered.

These first two questions should only relate to services or good purchased directly from the service provider. Many products carry their own warranties, like roofing shingles or siding. It's useful to know what these warranties cover as well as how long they last. The "warranty agent" question is important, because often warranty agents work with the manufacturer to get you repairs under warranty at a much lower price.

This is important mostly for larger jobs. Clearly a two man operation is going to build a home much slower than a 15 man crew. This is also a good indication of the overall size of the Plumbing company, if that's an area of concern for you. The reason you may want to ask about the fleet is that fleet size is a good indicator of the mobility of the company. Mobility may not sound important, but it's hard for the Richardson contractors to get to job sites if they lack appropriate vehicles.

Some companies may require a 10% deposit, some may not require any. For larger projects, you'll almost always need to give a deposit, and it's good to ask how much the deposit will be before going forward with a project. The Richardson contractor will know how much they need for a deposit when they've given you the estimate, so ask early.