Now first of all I got this model from the Google Website and there is one thing you should know.
If you want to use ROAS, CPA, maximize conversions, or maximize conversion value make sure you have enough conversions and test it!
If you do not have enough conversions I normally use Manual CPC.
Also If you want more profit, I would advise using POAS bidding.
Chose your bid strategy wisely 😉
