会場に着くと早速担当者に「この絵は将来必ず値が上がる」などとしつこく言われ、契約書にサインしてしまった。

「」、。

As soon as I arrived at the venue, a salesperson persistently told me things like 'this painting will definitely go up in value,' and I ended up signing the contract.

Literal

Venue [to-に] arrive-[discovery-と] right-away person-in-charge [by-に] 'this painting [topic-は] future surely value [subject-が] go-up' [etc.-など] [quotative-と] persistently was-told, contract [on-に] signed-[regret-てしまった].

A cautionary tale about pressure sales. ~と (discovery conditional) marks the arrival as triggering what follows immediately. しつこく ('persistently, annoyingly') characterizes the salesperson's approach. ~てしまった at the end signals regret: the speaker knows they shouldn't have signed. The quoted speech with など dismisses the sales pitch as typical patter.