I guess it depend on what you classify reviews and hype as.
I classify it into 3 tiers;
1. Reviews with clips/demos
2. Spoken/typed word reviews with little to no clips
3. No reviews, no clips, all hype; buying completely blind
I've rarely been able to play anything before I bought it. This is partially because of my taste in amps and partially because of the local market. What I'm looking for rarely comes up for sale locally so I'm usually having to purchase online. And there's been only one instance where I wasn't intending to purchase anything, popped into the store, played something, and went home with it. That's my Zinky Mofo.
Oddly, I've bought only a couple amps from Category 1 where there are enough clips and reviews where I can get a full idea of what I'm getting into. Anything I've bought from this category has been in the realm of expectation and I haven't been disappointed. Notable purchases here have been my Marshall Vintage Modern and Mesa Mark III.
Category 2 has been where the bulk of my purchases have come from. I like amps that are a bit off the beaten path; AKA not something you can readily purchase at Guitar Center. Usually there is just enough out there where I can get a general sense of the amp. That or people on RT who's ear I trust have been helpful. So far I've had a few surprises of expectation vs. reality, but haven't been disappointed in anything I've gotten. Notable purchases have been Monomyth Skeleton Key, Ground Zero Hellion, Laney Lionheart L50, and Fender Machete.
I've bought only 2 amps from Category 3 where the was zero [reliable] information and I purchased based purely on hype or reputation. These were what most would consider top tier amps so I felt the risk was very minimal. The 2 amps are my Naylor Superdrive 100 and Headfirst Alta. Most people hype the Naylor because of builder reputation, but few seem to have played one. As far as the Alta, I got in on the first batch so that was purchased purely based on Jason's reputation and ear for Marshall tones. I'm happy to say in both cases I was thoroughly impressed and they both remain in my top 5 favorite amps of all time.