I have not had any SAK springs snap 9I think..), but I have had some with weak springs, mainly older Wenger models.
I have also used the method of leaving the backspring tensed, by having the tools partly open, to weaken the springs on some slipjoints, so there is an effect on the spring from that. I also have some knives that are sold, in the package, partly open (Case) that have weak springs (they are locking, so it is not a huge problem)
Your best bet is to ask the seller to give you more information.
Funny story, last time I was at the dealer's I had a look at some knives and then, without thinking, closed them... I was then asked to open them, halfway again, as they need to have them in that, display position, for the customers.