"To go to the lengths of murder though there IS a risk. Why would Qualtrough put so much faith in a false address when he could have sent Wallace to a genuine address in the same area? He would have had adequate time to do what he had to do in the time Wallace would have travelled to and from Menlove Gardens."
I don't think it was conceived as a murder, but as a robbery. The false address bought more time, as they rightly figured Wallace would try at the other Menlove Gardens before giving up. It probably didn't make much difference in reality, but they thought it might, so why not include it the plan? Maybe it was just a personal touch, an extra wind-up for Wallace, part of a jolly jape that was only supposed to end in theft. Let's see if Wallace, the chess giant, can figure out how he's been had...