Hi Andy
Although smoke bombs will kill bed bugs there is no residual effect so eggs will still hatch and the problem will persist.
Having been involved in bed bug treatments in Uk I feel they could be dealt with reasonably easily if, as is common in Spain, there are not many soft furnishings. I will question if you feel you got bitten when visiting the property to view rather than overnight staying. Highly unlikely to be bed bugs if you were bitten during the daytime. Foul mite may be the culprits as they do bite during the day and often appear very small and black. Maybe the previous owners had pet birds or chickens??
Bed bugs leave black blood spots on the mattress or areas where they hide. This is blood they have taken for a meal then defacated around where they live. The previous writer was correct in identifying the most common harbourage age points.
Feel free to private message me if you need any more help or advice.
Bob
Former MD Pest Control Direct