Look at price suggestions at backpack.tf (prices are slightly outdated but shouldn't vary too much), steam market itself should show you some recent sale prices, although weirdly enough it appears to group all effect together.
Lastly, learn about scams: A "steam admin" will never ask for your items. If random person wants you to join/vote for their team on a website you never heard before, it's likely an attempt to steal your password, so don't try to login with steam on it.
Good luck!
Backpack classifieds: https://backpack.tf/classifieds?item=Well-Rounded+Rifleman&particle=31
Backpack stats: https://backpack.tf/stats/Unusual/Well-Rounded Rifleman/Tradable/Craftable/31
S.C.M.: https://steamcommunity.com/market/listings/440/Unusual Well-Rounded Rifleman