yes it is a real D as others have stated.
D models can come with the bayonet lug ground off neatly or intact , it depends on who the importer was and the specifics of how they wanted the rifles to appear.
The bolt carrier with no stripper clip guide is also a key feature on most but not all genuine D rifles. I have seen both.
I'm sure guys here that are into the finer details of the SKS rifles can tell you who the importer might have been.
Looks to me like the tooling marks on the stock screw might indicate a stock refinish but otherwise...... like a few others I may or may not have squirrelled away..... the OP's rifle looks awfully genuine to me. Whoever is telling you it is not obviously has a bigger mouth than thier knowledge or they are trying to set you up for a low ball offer. Probably the latter.
But here is an example of a BETA Arms import version and you will notice the intact bayonet lug and pin and the stock has the same features as the OP's
These rifles were all destined for the USA market until they werent ..... and were then offered to importers from Canada. Most but not all of my SKS collection came from Alan Lever in the early to mid 90's. You can see in the first pic that this rifle is not marked "SKS-D" as the OP's rifle shows. Still the Beta Arms 881 serial number rifles are genuine D rifles like the OP's but the importer chose the markings seen.
I'm tempted to pick up one of these new chinese sks imports but spare cash is not easy to come by these days. Truck parts for the restoration I'm doing are a bit more important right now