Make sure you visit a showroom and see just what you're buying. Examine its quality for yourself.
Consider:
Space required;
Cupboards, storage;
Worktop space;
Appliances;
Layout, arrangement;
Eating area;
Accessibility;
An island;
Flooring;
Pantry;
Lighting;
Colour, aesthetics;
Who'll be using it; the cook, or the whole family?
Other tasks done there: laundry, ironing, homework, entertaining?
Pets;
Do you need a table or will a breakfast bar do?
Will there also be soft seating and a television?
Would you consider building an extension or giving up a formal dining room to create a large kitchen/diner?
Wait until the vendor has visited your home before accepting a quote. Make sure you have a full quotation for the installation once they have made their survey. Some will be able to do structural work if needed, otherwise you will have to get a separate quote.
Ensure that you get a written schedule of payments. Never pay a deposit of more than 25% of the total contract value.
Companies that ask for full payment ahead of delivery have less incentive to deliver. Never pay in full until you have taken full delivery of your goods.
Some Terms and Conditions (the fine print) have expensive cancellation clauses. Don't sign anything unless you are prepared to honour your side.