1) "I shopped at Madisons for a pair of shoes." - I might have bought a pair of shoes there, but not necessarily. Maybe I just looked.
2) "I bought a pair of shoes at Madisons." - I definitely purchased shoes at Madisons. It must also be true to say that I 'shopped at Madisons', or else I couldn't have bought shoes there; but it might not be true that I had to 'shop around' - perhaps I knew what I wanted straight away.
Student or Learner