You just never know which unit might have a bed bug infestation.  Our dogs did indeed alert on the couch in the unit that complained about being bitten, even though this unit had been pesticide treated more than a month ago.
However, interestingly, the unit adjacent to it had a mid-size infestation, where our dogs alerted to both recliners.  The tenant, a nice old lady, informed us that she did not have any problems wih bed bugs.  It was obvious that she did not react to the bites of bed bugs.  Both recliners and the couch had all phases of bed bug developmental stages.
It is believed that 50% of people do not react to bed bug bites.
So if you suspect bed bug bites, don’t be afraid to call us at 508-713-8267 for a K9 inspection to confirm or allay your fears.