1. What type of documentation relevant to the eligibility criteria of the tenderer needs to be attached to the proposal as in the respective section ( Eligibility Criteria) refers only the criteria and not any specific documentation?

Correct Repetition: 

Kindly provide as much financial documentation as you deem essential to validate your professional background. Specifically, we require tax declaration from the past three years with an overall turnover of minimum 15.000 euro. Please also advise section 7: Selection Criteria.  If unavailable, the applicant can submit both a tax office commencement certificate (βεβαίωση έναρξης εργασιών από την εφορία) and an employer-issued experience certificate (βεβαίωση προϋπηρεσίας) from a comparable role.