The test items obtained at the vendor could all be of max rolls.
This way, the full potential of the items can be tested, rather than test with a random roll.
This way the feedback from all the testers will be on the max possible power of the item (excluding build & re-configuring)
The reason why I suggested max rolls is, say one player will give feedback that the item is bad while the other might say its op (extreme scenarios). Because of random rolls.
So to get the best feedback data, the prototype should be of same value/power for all testers.
I would even go beyond this and suggest to give a set of static items with fixed stats, no recal/craft & no loot/drop, to even more restrict the difference in feedback data.
But that will be too much & stop testers from testing different build & stuff.
But a set of fixed prototypes to start with will be better in terms of getting more realistic feedback. If it's reconfigured it varies ofcourse and the data should be less relevant.