If you buy vote so your post will payout, isn't that a lost of 50% of your investment?

Some bid-bots, especially @booster, give you a vote that is profitable - i.e even after 50% curation comes out, you will still make more than your bid from the vote.

Real example:

This screenshot shows the last round of @booster votes. The amount on the left was the amount the author paid, the amount on the right is the value that was voted. It does say 'Estimated Value' but that value is pretty accurate. I've highlighted the highest bid here, but as you can see everyone made a profit even after curation would be taken out.

Here is @booster's api link where you can see current round and previous rounds, and the countdown to when the next vote will be.

You can also send in a bid right there, on the top right is a button Add Bid click it and this screen will pop up:

Once you put your STEEM name in, a list of your eligible posts will populate (the green link there), so then input your bid and click the link for your post and it will populate in the URL area, submit and then wait for the round to close and you'll have your vote!

((Same idea when you use steembottracker, it's a little more involved over there as there are more bots to see, but I can explain that too with screenshots if you can't figure it out, just let me know. ))

Regarding @booster - Keep in mind that bids in the current round (not shown in my screenshot) will show the bid amount with an estimated value being the same as the bid (the amount on the right will match the amount on the left) - it is not until the round completes that the real values will be shown (like in my screenshot).
This is because the 100% vote weight of @booster is split up based on the amount of the bids. If you bid the highest that round you will receive the highest voting weight, so the value can't be truly estimated until all bids come in/round countdown is up. Each 'round' of bids last 2 hours (I like to submit a bid closer to the end, and I generally wait until 'quiet' rounds when there hasn't been a lot of bids.)

Some bots operate that way - some are 'on-demand' meaning they will vote as soon as you send them an appropriate bid, they will pro-rate their vote weight based on the amount you send.

For example, @givememonsters is an 'on-demand' se-token bid-bot. You send between 1-10 DEC and get a vote immediately (or soon after) (DEC is Splinterlands token) With 10 DEC being the max you can send, it gives you a vote of approximately 0.30 cents (so 0.15 to author) - if you send less than 10 DEC then the weight is given proportionately (so 1 DEC would give a vote of like 0.03 cents).

Most bots do not give a profit after curation, some only give a profitable vote after sending them a larger amount of STEEM..

You see, truly, the purpose of bid-bots is supposed to be for post promotion - basically giving you a large enough vote to get your post on 'Trending'. It's like advertising in a way, and advertising is not supposed to be free, let alone profitable - except for giving you exposure that may give you profit in the form of more eyes on your product leading to more sales (or upvotes in this case).

People have a problem with the fact that some bots are profitable and let's face it, people are using them for profit more often than they care about getting on trending. (SOME do use bots for the promotion, for their post to get attention. I have seen that genuinely being the case sometimes)

Let me know if you are confused still about anything :)

Oh! Edit to add: You can also send any bot a manual bid, or in the case like the @givememonsters bot.. Basically you send in your STEEM/SBD/se-token to the bot via your wallet and include your post link in the memo field (I always change my links to use steemit.com as some bots don't recognise other front-end links)