I'll guess 'pain shopping' is taking on the Victim role in a Drama Triangle. If it means something else, will you describe how you're using the term?
BSes experience so much pain that I doubt pain shopping is even possible in the first year or 2 that one knows one has been betrayed - it's all pain, almost all the time. No need to shop for more.
In the end, the only resources we have to determine truth from fiction are our thoughts and feelings. It's up to each of to decide what we believe.
So, noticing that one has no more answers may, in fact, be 'it.' My reco is to be open to new questions, though. Hell, I'm almost 14 years out from d-day, and I asked a totally new question in the recent past. My W continues to answer honestly, even if the answer is, 'I don't remember.' If IDR is the answer, though, she'll say that the answer probably would be something like _____, and she'll fill in the blank.
*****
I went into Q&A the way Oldwounds did, asking anything and everything I could think of. I did so because I thought the answers would lead to my understanding why my W cheated, and because I thought that understanding leads to healing. I ended up knowing my W's POV, but I still don't really understand how she let herself fuck up so badly.
What the Q & A really did was the following:
helped me recalibrate my ability to tell when my W was truthful or not -
each answer helped rebuild healthy bonds -
each answer helped rebuild trust -
each answer helped her take responsibility for her actions -
each answer showed she was open and honest (finally!) -
each answer showed she was committed to her own healing -
etc., etc., etc.
So the Q & A did help me heal, but in a way that was very different from what I expected.
*****
Trust your gut. It may be wrong - if your WS is a better liar than you think they are, you may very well be wrong. As long as you ask the questions that scare you, and as long as there are no important questions that you're hiding from, the gut-level sense that you know enough is a good sign. Not a perfect one, but very good.
*****
Now, if you do know everything you need to know, what's your next step?
If you're uncertain about your next step, what do you need to learn?