estuvieron probando
-they/you were trying
Pretérito progresivo para el sujeto ellos/ellas/ustedes del verbo probar.

probar

Significa que contantemente estuvieron probando anuncios hasta encontrar la variación correcta para esa palabra clave.
It means they were constantly testing ads until they found the right variation for that keyword.
Palabra del día
el villancico