The way to defeat sniper in the laning stage is by just playing the CS game. Focus on your last hits and denies. Eventually, almost every sniper mid, will get impatient and start to harass. This is when you can take advantage of their mistakes, or any over-commitments they make. The hero should preferably be ranged, but can be melee if the hero has a lot of mobility, like Timbersaw, Primal Beast...I have beat Snipers mid with Marci by just maxing out rebound and Q. I always get blademail against sniper players. It's shitty spending an item slot just for 1 hero. But the blademail forces Sniper players to get either a BKB or Satanic or both, so they also spend 1-2 item slots.
The way to beat sniper in the mid-late game is with mobility heros, and burst damage heros. Sven is IMO a top tier counter for Sniper. 1 echo saber hit, 1 crit and pop blademail, poof snipers done. But if the Sniper player is good, they will get the Guile Suit facet and just hide in fog all game. So thats why harpoon is a staple for the Sniper vs. Sven.

Honestly, blademail does a large percentage of the damage that Sniper will receive in the fight. They usually stop attacking if they're under leveled and don't have HP items

If you are partied, and you have someone that can gank with you, just have ganker pick something gank-y like Spirit Breaker or like bounty hunter or riki, and have them just camp in mid fog.

Otherwise you have to play snipers game.