[RPG] In the “Buying Magic Items” downtime activity, can I roll on a more affordable table than the Charisma/Persuasion check would normally indicate


In our current campaign we're nearing a point where we will be allowed to use the downtime activities from Xanathar's Guide To Everything for the first time.
After discussing with our DM, we've agreed to use Xanathar's rules for buying, selling and crafting magical items, potions and spell scrolls. After running a few simulations on the Buying Magical Items activity, I've noticed a potential issue that we may have. The rules state:

A character seeking to buy a magic item makes a Charisma (Persuasion)
check to determine the quality of the seller found. The character
gains a +l bonus on the check for every workweek beyond the first that
is spent seeking a seller and a +1 bonus for every additional 100 gp
spent on the search, up to a maximum bonus of +10.

Naturally, my first instinct is to have our Paladin with a +8 on Persuasion roll and taking the average of 10 on his check he ends up with a total of 18 without any additional bonuses. With a slightly higher roll or some bonuses gained from spending more gp or time on the activity, he can easily reach 20+
The tables he gets to roll for magical items depending on his Presuasion result, as stated in Xanathar's are the following:

1 – 5: Roll 1d6 times on Magic Item Table A.

6 – 10: Roll 1d4 times on Magic Item Table B.

11 – 15: Roll 1d4 times on Magic Item Table C.

16 – 20: Roll 1d4 times on Magic Item Table D.

21 – 25: Roll 1d4 times on Magic Item Table E.

26 – 30: Roll 1d4 times on Magic Item Table F.

31 – 35: Roll 1d4 times on Magic Item Table G.

36 – 40: Roll 1d4 times on Magic Item Table H.

41+: Roll 1d4 times on Magic Item Table I.

Based on my calculations, the tables most likely to come up are D and E, since to get a 15 or less, he'd need to roll a 7 and that's assuming he's not getting any bonuses. F is certainly possible if we spend enough gp or time to get him a substantial bonus.
"Great!" I though, this should be get us some cool magical items. So I went looking for my DMG to check what items are listed in those tables and then I realized how wrong I was. Just for reference, my two simulations which landed on tables D and E, resulting in the following items (all following the rules from Xanathar's about how many times to roll on each table and what price to give to the items):

Spell Scroll Level 8: 20.000gp

Potion of Storm Giant Strength: 135.500gp

Potion of Superior Healing: 20.000gp

Potion of Speed: 15.000gp

We are a party of 5, level 10 players, with a current total of about 30k-40k gp, without calculating the rewards we should get once we reach town for our now completed quest. To buy any of these items, more than one person would have to contribute to the purchase which could create issues with who gets to use the item (although we can talk this out and see who would benefit more and recompense the other players that contributed) and of course would put a huge dent in our treasury for a single consumable, 1 use item.
Yes, the spell scroll could be copied to our Wizard's (my character) spellbook for multiple uses but my highest spell slot right now is 5th level so it would be a long time before I can even get to use such a spell, and that's assuming it's a spell I can cast in the first place.

My original goal for using this downtime activity was to purchase some low level healing potions (none of us has proficiency with a herbalist kit to craft them) or possibly gain a magical item and while this is certainly possible, it is unlikely as I see it.
We could attempt this downtime activity with multiple people, hoping someone would roll low, or with people that do not have a high Persuasion but again this is situational. Taking this activity for multiple workweeks is probably not an option since we are unsure how much downtime will be available to us as we are already following hooks to the next plot and we are only taking this time to rest in preparation of our next undertaking.
I would also like to avoid having multiple people attempt this downtime activity as it limits our options for research on our next target location, and quite frankly, not everyone will want to do the same thing.

So my question is, is anywhere in the rules stated that we can decrease the total of our Charisma (Persuasion) check so as to roll for items in a lesser table for magical items that would be more affordable to our characters or should we just accept an unaffordable result as "tough luck"?

Best Answer

This is explicitly permitted:

.. you can roll for items from any table associated with a lower total on the Buying Magic Items table. (XGtE 126)

You can also find rules for searching for specific items a few paragraphs down.