At a minimum set up a dummy account so reviewers can quickly check out the basic functions of the site.

Unfortunately, that won't help with users, who will have to go through the signup. That is where properly conducted user testing, a task list, observation and analysis comes in.

You might find people don't use the site the way you think they should. Or find some procedure is unnecessarily difficult. Or layout difference which seem superficial, but make sense for those trying to actually use the site.

For example, should I sign in, enter all my data only to find how unusable the wishlist feature is? Someone sets up a wishlist, and I want to see it and maybe get something for them. How to I tell if they are a member on the site first? Liquidation implies limited supply and time sensitivity ...how does that work with a wishlist function???

And do reviewers have the time to run down a list of twenty or fifty different items after spending the time to go through a signup procedure?