How can my competitors effect my website to bring it down in Google?

It looks like some one does something against my website. Is this possible?

 

The standard answer is no - else everyone would do it to their competition.

That being said, I am sure there are ways to do this, on the short term at least.

I have done things to my sites that caused a negative impact. These were off-page so could have been done by a competitor.

 

Not really. I mean I presume someone could link to your site from a whole pile of spam sites, or sites distributing malware, but I don't think anybody knows for definite if this would harm your site, or if Google just discounts those links. They could also report your site for any number of reasons to Google, but that effect is only temporary IMO.

More likely if your site is receiving less traffic its to do with Google's own ranking changing.

 

Ahh I think it is possible for different themes I mean to say if you have travel site they can compete them in offering great schemes and great offers.
And Generally if your site has good number of links than no one can harm you, Google does not consider who is linking to you, you can get more answers or suggestion on similar thread

http://forums.digitalpoint.com/showthread.php?t=1438607

 

I think, it is impossible. if your competitor grows and you falls means, your competitor may creates quality back links to his/her site. That may cause your site goes down. Just deeply analyze the reason for negative impact of your site.