Dear Rsuh,
The selection of the vendors is depend on the materials, what is RFQ is for then you need to go for the same supplier, instead of going any general trader.
Example - If you have request for steel, then please select multiple steel supplier which is isi, iso standard, then request for quotation, then select accordingly, by quality,price and delivery period.
And please note highest price vendor is not a winner. Select lower price vendor but quality and delivery should be acceptable.
Thanks,