Toshiro wants to increase the conversion rate of his Shopping campaigns without increasing his budget. He should use:
enhanced cost-per-click (ECPC)
target return on ad spend (ROAS)
target cost-per-acquisition (CPA)
Maximize clicks is an automated bid strategy that sets your bids to help get as many clicks as possible within your budget. A Maximize clicks bid strategy works the same way as automatic bidding, with the additional option of being set up as a portfolio bid strategy.You can set a cap on bids for any keywords, ad groups, or campaigns when using a portfolio Maximize clicks bid strategy. It lets you control the maximum amount you’re willing to pay for each click.
Read more here: https://support.google.com/partners/answer/6268626