There are definitely ways to test display performance, such as the common PSA (public service ad) test to determine view-through contribution.
That said, I'd be careful painting all agencies under the same brush. There are plenty of CPA/performance-based agencies out there now, plenty that are flat fee-based, and every shade of gray inbetween.
Ultimately, ad agencies are incentivized to retain their clients, and if they have performance-based clients, just spending their money with nothing to show will not keep them in business very long. Likewise, people assume most brand advertisers at big companies are stupid. First off, you can't be a "big brand advertiser" without a "big brand" which means "a ton of cash." This also means they have fairly savvy and advanced statistical methodologies and research groups in place to help measure overall lift. Marketing mix modeling (MMM) is their lifeblood. Sure some of them have idiots working there, but at a certain point you have to look at the data at a higher level because you simply can't track everything you do in an accurate manner. Doesn't mean there isn't a way to observe lift and attribute it.
That said, I'd be careful painting all agencies under the same brush. There are plenty of CPA/performance-based agencies out there now, plenty that are flat fee-based, and every shade of gray inbetween.
Ultimately, ad agencies are incentivized to retain their clients, and if they have performance-based clients, just spending their money with nothing to show will not keep them in business very long. Likewise, people assume most brand advertisers at big companies are stupid. First off, you can't be a "big brand advertiser" without a "big brand" which means "a ton of cash." This also means they have fairly savvy and advanced statistical methodologies and research groups in place to help measure overall lift. Marketing mix modeling (MMM) is their lifeblood. Sure some of them have idiots working there, but at a certain point you have to look at the data at a higher level because you simply can't track everything you do in an accurate manner. Doesn't mean there isn't a way to observe lift and attribute it.