Those are all totally reasonable things to ask if they're sourcing their baby strollers from some random factory located in a country where safety standards are

Those are all totally reasonable things to ask if they're sourcing their baby strollers from some random factory located in a country where safety standards are not what is expected where you're selling them. If the retailer saving money because the factory they sourced their product from is not testing adequately then obviously the retailer is shouldering that risk and becomes the responsible party. They don't necessarily need to do the testing in house, they could outsource it, but ultimately the cost of testing should be borne somewhere in the supply chain, before it reaches the consumer. And honestly, this should be better for the retailer than sending them into the outside world untested and then having to do some big recall operation when, in this example, either a parent spots the flaw or the baby stroller collapses on their child.