We recently ponied up to the counter to collect our booked Avis rental at IAH (Houston TX USA). The agent tried to upsell us from a VW Jetta or similar to ‘an SUV’ for only $3 per day more. Preferring what we booked we declined. The agent then admitted they did not have any Jettas or similar left and we got the ‘SUV’ (a Jeep Wrangler) at no additional cost. Despite using more fuel it was good fun for the 5 days we had it - AND it did not break
What might sound attractive or even too attractive could be a CYA to extract a few extra dollars per day just because they can. Be cynical about the motivations they may have to upsell. This trick seems universal.