If as one of criterion indicators "business reputation" the customer establishes membership of the participant in the self-regulating organization (SRO), it can be recognized as restriction of number of participants of purchase.
The participant has the right to submit the certificate of SRO membership in which isn't obligatory. However existence of this document doesn't mean that the participant has higher qualification, than the others, and can offer the best conditions of performance of the contract. Besides, the introduction in SRO demands time and financial expenditure.
Document: Letter of FAS Russia of 08.10.2015 N ATs/54940/15