I broke even on the flip, but because I had to take out a loan against my 401K, I wasn't able to pay it back in time and ended up losing all of my 401K savings and paying taxes and penalties.

The key is to approach it as a conversation given you don't want to lose them.

On the other hand you may lose on a good rental property that is already or has the potential to cash flow regardless of price.

On a larger scale, how do you protect yourself from losing any money when submitting offers on deals that you need to back out of (any and all contingencies). 

I've tried various things: shorter inspection time period (typically it's 10 days here, and if you do a 3 or 5 day inspection time you can be attractive b/c the seller can get it back on market quicker if you find something you don't like during inspection period); non-refundable earnest money (maybe $1000 of money that you will not get back for any reason on your side - not if the seller breaches-- should the offer not go to completion - this shows you are an extremely interested buyer, but you could lose the money, so use cautiously and with the advice of your agent who knows how to correctly write that into the contract); put a limit on the repair request no required by lender - cap it at $0/as-is, or $500; a higher earnest money - like $5000, shows you are serious.

Meaning 90% are unhappy and would have opted to not enter the venture.   

They are valued based on comps and not NOI / Cap Rate, so you lose the ability to drive appreciation, and if you cannot find good comps, they can be hard to refinance or sell.

You lose no matter what. 

Will you lose $30k of credit or will you still be able to have the $50k of credit?)

On the umbrella, the question for you is: Am I OK with losing all that I have if I am sued?