I would get a deposit in my account when the PM collected the rent, and I would cut a check to the MH park and mail it.

If you are worried about it you could always ask for the 2x or 3x security deposit (or max allowed for your state).

Get the decision-makers or influencers some cash and their ear.. then lastly, there's bumping up the purchase price if it makes sense..3) Tighten/eliminate contingencies to your comfort level, shorter close4) Offer a small non-refundable deposit, to show them you're serious about it, and not just fishing around, with no money on the line5) Provide asset statements showing you have plenty to cover it, even if you don't plan on going higher or even paying cash..6) Send a letter with your asset statement demonstrating your track record, your plan, cash to do it, that you're comfortable so far etc..

What I mean is, Find a seller, make an offer -> put a little bit of cash down as a deposit -> then have a buyer wanting to buy the house.

Yes the husband is the sole owner of the apt on the apt share holder. and the wife is not. however as far as i know, the wife is also getting half of the sale.What i am worried is can we walk without getting deposit taken.

Where we lived in China, for example, it is common practice to collect 6 months to a year of rent up front not including the security deposit.

In this model, the custodian/administrator holds the funds and you will instruct them to take action on behalf of your IRA, so they sign every document, cut every check, receive every deposit, etc. 

Same way security deposits go into escrow accounts.

(this makes sense, a 4.625 yield compounded annually over 14 years on a $300 monthly deposit generates me about $20,300 of interest, I checked with a calculator like this one) Returns on my Roth IRA are (maybe) 7% per year.

Charge the full month, then give them back anything/prorated if they vacate before the end of month along with their security deposit.