Does ASTM certify products or grant a seal of approval? What certification services does ASTM offer?

Yes, ASTM certify product during approval.

Specially, in case of Plastic manufacturing company always follow to ASTM standards for testing reason as a international standard. Mostly FM approval, BSI Kite Mark, these are suggest to prepare any sample or testing regarding to ASTM during certification/approval.

They are suggested for ASTM-D, ASTM-F standards.