Hive account@randowhale and Hive account@worldclassplayer have turned $1 into $1+ in up-votes every time I used them, but the latter seems to be hanging up the boots for at least the short-term. I've had mixed results from Hive account@bellyrub. Other accounts seem to be popping up daily to provide a similar service and some are scams of course, so it's probably best to find other STEEM posts first confirming if they are worth it or not. Keep up the good posts!