Most treatments that need redoing did not fail because of the product. They failed because of something that happened in the days before or after the visit. None of it is complicated, and knowing it in advance saves you a second appointment.
Start with what to do. Clear the worktops and cover or put away exposed food. You do not usually need to empty cupboards — a technician treats hinges, runners and voids rather than shelves — but they do need to be able to reach the backs and edges of units. Pull furniture a little away from walls in the rooms being treated, because skirting junctions are where a great deal of the work happens.
Give the technician a list before they start: babies or young children, pregnancy, anyone with asthma or respiratory problems, pets, fish tanks, birds. All of these change what gets used and where, and it is far easier to plan around them than to work around them halfway through.
Tell them the history too. What you have seen, where, at what time of day, how long it has been going on, and what you have already tried. Someone who mentions they sprayed the kitchen twice last week is giving their technician genuinely useful information, not confessing to something.
Now what not to do. Do not spray retail insecticide in the days before a visit. For bed bugs it scatters the infestation into new harbourages and turns one room into three. For cockroaches it leaves a repellent residue that makes bait placements unattractive and delays the treatment by a week or more. If you have already sprayed, say so.
Do not deep-clean immediately after a treatment. Washing skirting, wiping down inside cupboards or mopping treated areas removes the residual product exactly where it was placed. Your technician will tell you which surfaces to leave alone and for how long — usually a fortnight — and normal cleaning everywhere else is fine.
Do not remove bait placements because they look untidy, and do not clean the ant trail after baiting. The trail is the delivery route the bait uses to reach the nest. Removing it restarts the problem you just paid to solve.
Finally, expect activity to increase briefly after baiting. Ants and cockroaches recruit to a new food source, so the day after treatment can look worse than the day before. That is the treatment reaching the colony. It is also the moment when people most often reach for a spray and undo the work. Give it a week.
If something still looks wrong after that week, call rather than treating it yourself. A follow-up visit is included, and the information about what happened in between is what makes the second visit effective.