Stock
Allow availability to weigh in without ignoring the query.
Stock is important, but a less relevant product does not automatically get better because there is a lot of it.
Availability
Use current stock or availability as a signal.
Sold out
Lower or label products when return is uncertain.
Alternatives
Send to relevant replacements when relationships are known.
Local stock
Keep store and market context separate.
Measure effect
Check CTR, conversion and cancellations after ranking changes.