I am quoting a phrase of Martin Dyer in his paper Approximate Counting by Dynamic Programming:
Since 0-1 knapsack is self-reducible, existence of an fpras for the problem now follows indirectly from a general result of Sinclair and Jerrum[19]
In that paper of Sinclair and Jerrum it is stated that:
It follows that, for self-reducible structures, polynomial time randomised algorithms for counting to within factors of the form (1 +$n^{-\beta}$) are available either for all $\beta \in R$ or for no $\beta \in R$.
Question 1: Does statement 2 mean that counting self reducible structures might have an FPRAS?
Question 2: What is the indirect method Dyer is talking about? Is it some folklore method considered well known?