Check to see if the advertisement carries a full bona-fide postal address, including the postcode. 

Check the Royal Mail database if you wish to check if the address exists, even then it may be a private address or another business which is completely unrelated to TV Repairs. If you are not sure of the address, drive past and see if the repair shop actually exists.

Is the repairer an authorised service agent for any of the major manufacturers?

Does the advert carry a proper company name.

If you telephone the company to tell them that you wish to bring in a repair, are they happy for you to visit the address given in the advert or do they wish you to go somewhere completely different.

Does the company name, address and phone number given in the advert match the BT Phone Book listing?

Does the company leave you with a receipt for your set when they take it away?

When the repairs are completed and you pay for the repair, does the company give you a written receipt, using company stationery, fully detailing the work that has been undertaken?

Is the repairer happy to receive payment by cheque or card or do they insist on cash only?

Does the repairer state the period of the repair guarantee in writing?

Does the repairer give you one estimate, then offers you a second estimate after  you decline the first one, at a reduced rate.

Does the engineer who calls make any attempt to repair, examine or assess the equipment in your home or does he insist on immediately taking the set away.