Currently, there is no simple step-by-step checklist offered by google for merchants to guarantee a position on to any of the google-shopping lists, despite being asked many many times before; there is simply no such feature and the details have so far never been articulated publicly.
Results are mainly determined by the bid (budget) and quality over time.
Generally, any technique that google has indicated may help improve quality can also improve performance and will therefore, also increase the chances that a merchant will show within the left-hand-side lists on google-shopping.
Adjusting campaigns and budgets, especially ones that ensure that a budget is not depleted, is certainly one technique that will help with ad-rank and overall performance and may help improve the probability that a merchant may show within the left-hand-side seller-list.
Both product reviews and ratings and seller reviews and ratings are also
good techniques to improve overall quality and performance and therefore
greatly increases the probability that a merchant may be shown within the
left-hand-side lists over time.
Adjusting the title and description to be shown within a broader range of
search-terms can help impressions, quality, and may increase the chances
that a merchant will show within the left-hand-side seller-list — if that is the intended, or rather the only goal; however, this and other similar techniques may also have the unintended consequence of resulting in more clicks from less relevant or irrelevant searches and therefore potentially wasted clicks, and a decrease in conversions over time.
Also, the submitted data should match the landing-page data and many
automated systems use landing-page data to create an automated feed;
so, always consider changing the site’s landing-page first; especially since
a submitted title or description that is not essentially identical to the (link)
landing-page, displayed details, is a policy violation.
Many of the lists, other than the seller-list, are also influenced by item_group_id and the corresponding variant attributes — especially color, material, and pattern — and if these values are accurate with respect to the image_link details.
A best-practice is to always measure performance and overall results before, during, and after, making any such changes to the submitted data, the website, or the campaign.
However, google is constantly experimenting with all the various features and details within google-shopping — so none of these techniques will necessarily guarantee a position within any of left-hand-side lists, long-term.
A single search can sometimes result in hundreds or thousands of potential merchants but there is only room for 5-20 or so, depending on the context; even if google did not make any feature changes over time, a user’s interactions can greatly influence outcomes — especially which (left-hand-side) options are being selected by users over time, which search-terms are being used, and a user’s search-history over time, can greatly influence results.
What one user sees (in a seller-list) is not necessarily what another user sees.
Creating a new id simply forces a new product to be indexed — changing an existing product’s id value will remove its history. \
Duplicating any physical item listing however, such as by submitting
the same item with different id, is a policy violation and is grounds for a disapproval or suspension from the program, at any time.
Global-trade-data values (brand, mpn, gtin) must be submitted as assigned by the brand-manufacturer and any merchant manipulation of global-trade-data is also a policy violation and grounds for a disapproval or suspension from the program, at any time.
Any one serious violation, or any continued violation, of any policy can result in a suspension from the program, at any time — some suspensions are permanent.