I don’t think so, I’m pretty sure that Smart Shopping will always take preference if there’s two campaigns with the same product groups unfortunately.
The two ways to test that I’ve heard of are setting the standard shopping to run at a fixed budget for X weeks then setting up smart shopping for all product groups and letting that run for X weeks and comparing final ROAS of the two, or just taking it a product category at a time.
It’s not really possible to a/b those, as they run different networks. Standard Shopping is search only while Smart Shopping adds GDN ads into the mix both for new and returning users. Smart Shopping will always take priority as in if both campaigns are eligible and have same result for one auction, Smart will show. They don’t cannibalize if run on the same account – only one campaign enters final auction, so feel free to run them alongside. You can try to evaluate performance on a pre post basis.
Nope. The Google documentation specifically states that “smart” shopping campaigns will take priority over any other shopping campaigns. Even if you try and test by limiting budget, Google will just under-serve the smart shopping campaign. You also don’t get any settings options for smart campaigns that could possibly allow for any control on your part. Having more than one account would violate double serving. So you are either 100% in or, 100% out.