First mtb, no test ride just took advice from LBS, and it was fine
Second test rode in town for 10 mins, worked out fine
Third, test rode two back to back from same LBS as first, an hour on each. Worked out fine
Fourth, bought frame of classifieds without even seeing one in the flesh as it were, worked out fine…
Etc. etc.
To cut a very long story a bit shorter, only had one disapointing bike so far, I hadn’t ridden in advance, but three others bought blind second hand have been great, two bought new after test rides have been great, so either way can work