How dodgy would something have to be before you wouldn't count it? Lets try a multi-choice anser (ho ho!)
Unlikely as it may sound, imagine you noticed a fully winged unringed snow goose on your patch, sheltering under a gorse bush, trying to defend itself against irate golfers and their golf balls. Would you:
A) Grab the nearest mashie niblick and have a swing yourself?
B) Abandon all thoughts of birding and rush home to phone the RSPCA?
C) Attempt to catch the poor blighter, bring it home for questioning, leave it on the patio, and be amayzed when it proved its genuine rarity credentials by vaulting the 6 foot high fence?
That'll be option C then! Of course it is ok to tick this bird on your patch list!