Is it possible for any of the competitors for pull down my SERP ranking by spamming the website?
Generally, no.
Maybe, by posting your link on bad neighbors or something like that… but haven’t seen it really
How do you think that will actually harm a site?
Ever wonder why none of us are actually doing that to try and tank our competitors?
Matt Cutts said it also that those backlinks can be harmful.
Simply because I don’t know which are those sites lol Also I try to use the time to build my own backlinks not to tank a competition.
Nonsense. Care to show us where he said that?
Yes possible to down your site in SERP. Actually, the competitor will have more back links & have back links in all sites that you have. Its the fact your sites ranks down in SERP automatically due to the above reason.
Getting their own SERP up is not the same as getting your serp down!
Sure if they take you over you will go down, but that’s a side effect of them going up, and completely different from them doing anything about their own SERPs and getting your SERPs down, which is what the OP asked.
it is possible to track that you need to note down all your submission and collect your links compare both and remove where you don’t post
I don’t think its possible otherwise people will do this to each competitor and I don’t think Google is fool enough to allow it.