We have not done a survey within the last 6 years. If we are unsure about something like "how many weeks suppliers need to calculate for a specific event" we include this in the invitation email/letter.
We send out automated, but customized message after each event stage.
Thereby we are asking suppliers for feedback on system, process, event over all and our team involved.
In the last years, we do not get too much feedback.
Manytimes it's a praise on our work and documents provided. If there is criticism, than this is mainly on the price level seen in auctions. But occuring very seldom.
Additional feedback was also received e.g. on event set-up (Lot and Line Item structuring), but this tended to be more critical.
The problem is, that the suppliers do not know, what possibilities we have in the system - so they can not judge on this in an educated matter.
Eventhough supplier feedback did not prove to be very helpful to our organization, we'll keep on sending those messages and provide possibility to criticize/praise.
I would estimate we are inviting around 20.000 suppliers to sourcing events per year and potentially get around 10 designated feedback messages, most of them positive.