Whether it's a loss or not isn't the question that should be asked .. because you may have very well overpaid for it. Or if you were buying as an end user then there's a 50% chance any sale will be a loss.
The real question is how much is it worth. Which is an extremely open ended question because at the end of the day every person who sees a domain will see the value differently depending on their own perspective and experiences.
My current Portfolio Auction at Flippa
will very likely go at a loss .. but I'm fine with that .. some decent domains in there .. but over the last few months my portfolio has exploded in size. My goal is to get down to a size where I can fit all of them into the middle tier Efty account (1500) .. I have about 200 more domains to go. So what I learn from this auction will help me make more for future auctions. It's also letting me learn the auction system so there is added value for me there beyond what I'll make at the auction.
Most importantly .. it's better to even drop (or sell for any amount) names that have minimal chances of selling .. .xyz domains with hyphens for example .. lol. Seriously though .. there are an awful lot of truly horrible domains out there. It boggles my mind when I see the expiration lists at all the really bad domains that were not just registered .. but renewed for 3, 5, even 10+ years. Even here in the appraisals section .. at least 80% of the domains should never ever have been registered in the first place (and I'm being very nice with 80%).
So at the end of the day .. it's best to cut your losses upfront if you have a low likelihood of selling the domain.
If it's a good domain however .. then it's really a guessing game .. sometimes you might never get a better offer than the one that you have in front of you .. so maybe a small loss is better than nothing. But on the other hand you might get a 5x offer a week later. The only real way to judge is to know your domain and the targeted industry or potential end user.
That being said ... I've come to the realisation that domaining still has a very very large luck factor to it .. much of domaining after you purchase is out of your control. That's why value buying is crucial in domaining!