Problem with buyers being blocked from bidding

[2005lese]

Some of my potential buyers are getting this message 'You are unable to purchase this item due to restrictions from the seller. You have winning bids, submitted offers or bought 1 item(s) from this seller in the past 10 days. Please contact the seller for more information.' 

I dont know of any restrictions, where should I look?

[ruby*tuesday · Accepted solution]

You may have restrictions inadvertently set. Enter "Buyer Management" into Help and Contact at the very foot of the Page.

[2005lese · Accepted solution]

A Box that I did not know existed was ticked, many thanks

[john1297576]

You need to find this in Buyer Requirements and edit.