Rogue Traders rarely use a fixed landline phone number. Always check for a landline number not just a mobile and a business address.
Avoid any cold callers most reputable companies have worked booked in sometimes months in advance.
Always get a written quotation with a breakdown of materials to be used and check that all waste will be taken away and that the quote covers everything you have requested.
Never hand over full payment for any works prior to work starting, reputable business will ask for a deposit upon commencement of work and balance paid at the end of completion if you as the customer are satisfied.