Appraisal sites are scams. One hundred percent of the time they are scams. After all, if they weren't scams, they would offer you at least, say, 25 percent of their appraisal, but that never happens. Anyone who ever mentions an appraisal when talking about a name is not to be taken seriously.
The name seems decent. Without the German meaning, Spott.com seems to be worth having as a nice potential brandable name (that doesn't mean that you could always sell it quickly for XXX, as you still have to get lucky to sell any name these days). If it is a legit German word, then it could very well have strong value, and if it is a word that is actually used and understood by all Germans regularly, then you have yourself a good name.Dotcoms are always strong, even though Germany uses .de. That isn't the case for other extensions. Dotcom trumps all and is seen as legit everywhere. So, it has value to a German or American buyer. The American buyer would see it as more of a brandable, and the German will see it for the meaning, if ridicule is what it means in Germany.
Not all words are worth money, but if the word means ridicule, and it is used often in Germany, then that would explain your mid- X,XXX offer. Of course, it is always possible to get more, but the key is the get that without blowing the sale. Now, if a name truly has good value, then there is very little risk in blowing the sale. If someone wants it at 5K, and you ask for 8K, they should still want it 5K. Most domainers blow sales because they are selling worthless garbage, and sometimes the buyer sees through that and doesn't want to reward said scammer with a sale if the scammer asks for too much.
This name seems solid, so you have less risk of losing the sale if you ask for too much. If you scare them away with too high of a counter-offer, you might want to wait a few days or a week before dropping back down. It doesn't look good to ask for a huge amount, and then 30 minutes later take the offer. You have confidence in the value of your name if it truly has value.
I think your offer is probably legit, and that is real money, which means they want it. So, taking a shot for a nice chunk more is probably the right move, even if you run a small risk of scaring them off. If they offered 5K or so out of nowhere, as their opening bid, then you might be able to get 12-15K, or even more. Not many people came out of the clouds and offer 5K off the bat without the idea that they might pay a lot more. But if the 5K was a drawn out negotiation, then you might be close to the limit with this buyer. It isn't science, and you have to use your best judgement. If you are savvy at all, then you don't need much help from message boards posters.
It is an art, not a science, to extract as much as possible. But you can also offer someone a good deal without the world coming to an end. Good business involves offering a product as a reasonable price. You don't have to destroy everyone in your path like most domainers try to do.