You should not - that is what the price-beat is for. But compare what the numbers buy. The bargain job is a bracket screwed to whatever the drill hits first, leads clipped along the skirting, no insurance question asked, and a warranty that lasts as long as the drive home. Ours is the wall identified before drilling, fixings matched to it, cables concealed where the construction allows, public liability insurance, and on antenna jobs an Australian-made antenna with a 25-year manufacturer warranty. When the cheap job fails, the redo costs more than doing it once - we know, because redoing them is a steady part of our week.