Meta clients can have a custom logo next to their auction on both Google and Tripadvisor. Here are the requirements for adding your logos on metasearch.

Google:
Dimension: square, 300px or larger

Format: PNG

Size: no limit
Background: transparent background
Text: no more than 3 text characters (no more than three letters or numbers)
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TripAdvisor:
Dimension: 384 px x 164 px (WxH)

Format: PNG
Size: 6kb (min) - 12kb (max)

Background: logos should be optimized for white/yellow backgrounds (#FFD14F)
Depth: 32 bit with non-boxed logo against white/transparent background
Border: No additional borders around logos
Text: the logo should not contain any call to action or marketing text