Explanation:

- Let's analyze the jumbled parts:

- (P) "but perhaps the best way is to agree"

- (Q) "there are many ways of dealing"

- (R) "with them without excessive argumentation"

- (S) "with intransigent customers"

- The logical flow of the sentence starts with introducing a general idea or subject.

- (Q) introduces the topic, "there are many ways of dealing," which begins the discussion.

- (S) completes the subject, "with intransigent customers," detailing who is being dealt with.

- (P) provides a suggestion, "but perhaps the best way is to agree."

- (R) concludes with a method, "with them without excessive argumentation."

- Arranging these parts, the logical and grammatically correct sequence is QSPR.

So, the correct sequence is:

Option 2: QSPR