Switch positions? I'm not sure it's available (2,5)
I believe the answer is:
on offer
'available' is the definition.
(I've seen this before)
'switch positions? i'm not sure' is the wordplay.
'switch positions?' becomes 'on off' (on and off are positions on a switch).
'i'm not sure' becomes 'er' (expression of hesitation).
'onoff'+'er'='ON OFFER'
'it's' acts as a link.
(Other definitions for on offer that I've seen before include "is made cheaper?" , "available for less" , "At special price" , "For sale at specified price" , "For sale at a certain price" .)