The same place where you can buy and sell most things - the Grand Exchange or by an exchange with other players.
all you need to do to get poison off of a weapon is use a cleaning cloth.
Super strong weapon poison is the strongest (P++). It is made with nightshade and poison ivy in a vial of cocnut milk using the herblore skill.
Weapon wise you can poison any: - Arrows - Spear's/ Hasta's - Daggers - Javelins - Throwing Knives
Anti-Poison And/or weapon poison can be made using the Herblore skill ( provided you have the levels) or they can be bought off another player.
Weapon poison, it depends on what type:Weapon Poison: 346 - 383gpWeapon Poison (+): 734 - 811gpWeapon Poison (++): 4,661 - 5,152gp some players might buy it for more some players might buy it for less,the price above may not always be correct as the market for those items can vary if you would like the full and current price go on to http://www.runescape.com/ and click on game guids and then grand exchange or just go there on runescape manually.
poison+weapon poison is snake+weapon(or tools) weapon is tools and human
weapon+poison
If you have the right herblore level you can make the potion, otherwise you will have to buy Weapon Poison in the Grand Exchange, then use the potion on your dagger to poison it.A guide to getting the best weapon poison:Weapon Poison = Cheapest and weakest of the three.Weapon Poison P+ = Moderately Priced, Better than Original Weapon Poison damage wise.Weapon Poison P++ = Costs slightly more than P+, better that Weapon Poison P+ damage wise.If you want the best value for your money, get P++ its the best of the 3 and should cost somewhere under 10k.
Poison + weapon = poisoned weapon
poison+weapon poison is snake+weapon(or tools) weapon is tools and human
Mix snake and weapons.
no you can not sell your house on runescape.