Generally small jobs, under £100 I give estimate over the phone, most people dont know sizes of carpets so I always say:
"Without seeing it, to give you a rough idea of cost, a standard 2 -3 bedroom 4yd x 5 yd living room carpet will cost in the region of £XX"
We work on standard prices for upholstery so they are easy to quote over the phone, some are easy jobs and you are quids in, others are nighmares, but at the end of the day they balance each other out
If the job is close by or I am passing, I will always call in and quote face to face, the success rate is much much better. Commercial is ALWAYS a visit
You will always find people who just phone and want to know the price, they don't want you to come around, they want it done for next to nothing and are just phoning around. How many of us get daily calls wanting to know the price of cleaning a 3 piece or carpet an when you give them the price its a case of "I'll need to speak to the wife/husband and get back to you" never to be heard of again.