We had a visit from a lady representing this company yesterday (Red Ball in fact) - she showed me her ID and told me they had representatives looking at outside walls of pre-war houses as they often needed treatment.
Fortunately I remembered this thread and told her to look at the SE23 forum because her company was clearly not well regarded.
She looked taken aback. After closing the door, two minutes later, her "manager" was there looking a bit aggressive. I repeated, pleasantly, what I had told the young lady.
My husband's bellowing in the background got rid of him but the pleasant patter could easily take in someone so just to be aware that they are in the area.
They appear very plausible.