You are not actually "buying points" at $7 to $10, you are renting a reservation from a
DVC member. You have no control over those points whatsoever, the DVC member, if unscrupulous, (though admittedly very rare) could cancel the ressie at anytime. Non-members are not allowed to speak to member services to verify the ressie. You can not cancel or modify the ressie through member services, that can only be done by the member. BTW, while possible, it is the exception to be able to rent a ressie for less than $10 per point, and the "normal" rental price seems to be leaning more towards a slight increase. And if the transaction does" go bad" Disney will not intervene, it is a private transaction between you and the member.
The initial $85 to $100 buy in means YOU are a member, you control your points, you will hae points available to you for reservations year after year, until you either sell the contract or the DVC contract ends in 2042 or 2054 (depeding upon which resort you purchase in). You will have to pay annual dues, wich includes maintenance, taxes, resort management fees, etc. They currently are averaging less than $4.50 per year, but can increase. They have, on occasion, even decreased, but given the increases in insurance, employee and security costs, they have increase lately.
While actually owning the points isn't for everyone (no timeshare is "one size fits all") it will certainly save you money in the long run over renting, and allows you not to go on the "trust factor" when trying to deal with a rental situation.